In file included from Curl.xs:581:0:
curlopt-constants.c: In function 'constant':
curlopt-constants.c:19:58: warning: 'return' with no value, in functio
+n returning non-void
             if (strEQ(name, "DID_MEMORY_FUNC_TYPEDEFS")) return CURL_
+DID_MEMORY_FUNC_TYPEDEFS;
[download]

#include "curlopt-constants.c"
[download]

#undef CURL_DID_MEMORY_FUNC_TYPEDEFS
#define CURL_DID_MEMORY_FUNC_TYPEDEFS 0
#include "curlopt-constants.c"
[download]

Thank you, Rob, I almost missed the one issue that got fixed: I no longer get:

./curlopt-constants.c:19:58: error: non-void function 'constant' shoul
+d return a value [-Wreturn-type]
            if (strEQ(name, "DID_MEMORY_FUNC_TYPEDEFS")) return CURL_D
+ID_MEMORY_FUNC_TYPEDEFS;
[download]

I applied this patch to Makefile.PL:

ref: https://rt.cpan.org/Public/Bug/Display.html?id=117793
ref: https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/perl-modules/WWW-Curl-4.17-Skip-preprocessor-symbol-only-CURL_STRICTER.patch

CPAN RT#117793

Signed-off-by: Petr Písa&#345; <ppisar@redhat.com>
---
 Makefile.PL | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile.PL b/Makefile.PL
index f9170bb..ad2bd3d 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -127,7 +127,7 @@ if (!defined($curl_h)) {
     close H;
 
     for my $e (sort @syms) {
-       if($e =~ /(OBSOLETE|^CURL_EXTERN|_LAST\z|_LASTENTRY\z)/) {
+       if($e =~ /(OBSOLETE|^CURL_EXTERN|^CURL_STRICTER\z|_LAST\z|_LAS
+TENTRY\z)/) {
           next;
        }
        my ($group) = $e =~ m/^([^_]+_)/;
-- 
2.7.4
[download]

That got me past an error free make and make install, yay! (Oddly, implementing the patch by hand did not work, but I wanted to learn how to automatically apply them, so I researched that.) When I patched the code with:

patch -b < WWW-Curl-4.17-RT117793.patch
[download]

... I was able to successfully make install the code.

I *am* still getting 4 warnings during my make (make test), I am not sure if those are of concern or not:

[ns3:~/src/WWW-Curl-4.17] administrator% sudo make
Skip blib/lib/WWW/Curl.pm (unchanged)
Skip blib/lib/WWW/Curl/Form.pm (unchanged)
Skip blib/lib/WWW/Curl/Share.pm (unchanged)
Skip blib/lib/WWW/Curl/Multi.pm (unchanged)
Skip blib/lib/WWW/Curl/Easy.pm (unchanged)
Running Mkbootstrap for WWW::Curl ()
chmod 644 "Curl.bs"
"/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/bin/perl" "-Iin
+c" "/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/5.24.0/
+ExtUtils/xsubpp"  -typemap "/Users/administrator/perl5/perlbrew/perls
+/perl-5.24.0/lib/5.24.0/ExtUtils/typemap" -typemap "typemap"  Curl.xs
+ > Curl.xsc && mv Curl.xsc Curl.c
cc -c  -I/usr/local/Cellar/curl/7.58.0/include -fno-common -DPERL_DARW
+IN -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/i
+nclude -DPERL_USE_SAFE_PUTENV -O3   -DVERSION=\"4.17\" -DXS_VERSION=\
+"4.17\"  "-I/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib
+/5.24.0/darwin-2level/CORE"   Curl.c
In file included from Curl.xs:574:
./curlopt-constants.c:176:56: warning: implicit conversion from 'size_
+t' (aka 'unsigned long') to 'int' changes value from 1844674407370955
+1615 to -1 [-Wconstant-conversion]
            if (strEQ(name, "ZERO_TERMINATED")) return CURL_ZERO_TERMI
+NATED;
                                                ~~~~~~ ^~~~~~~~~~~~~~~
+~~~~~
/usr/local/Cellar/curl/7.58.0/include/curl/curl.h:1969:31: note: expan
+ded from macro 'CURL_ZERO_TERMINATED'
#define CURL_ZERO_TERMINATED ((size_t) -1)
                              ^~~~~~~~~~~
In file included from Curl.xs:574:
./curlopt-constants.c:2142:44: warning: implicit conversion from 'unsi
+gned long' to 'int' changes value from 18446744073709551599 to -17 [-
+Wconstant-conversion]
            if (strEQ(name, "ANY")) return CURLAUTH_ANY;
                                    ~~~~~~ ^~~~~~~~~~~~
/usr/local/Cellar/curl/7.58.0/include/curl/curl.h:708:32: note: expand
+ed from macro 'CURLAUTH_ANY'
#define CURLAUTH_ANY          (~CURLAUTH_DIGEST_IE)
                               ^~~~~~~~~~~~~~~~~~~
In file included from Curl.xs:574:
./curlopt-constants.c:2143:48: warning: implicit conversion from 'unsi
+gned long' to 'int' changes value from 18446744073709551598 to -18 [-
+Wconstant-conversion]
            if (strEQ(name, "ANYSAFE")) return CURLAUTH_ANYSAFE;
                                        ~~~~~~ ^~~~~~~~~~~~~~~~
/usr/local/Cellar/curl/7.58.0/include/curl/curl.h:709:32: note: expand
+ed from macro 'CURLAUTH_ANYSAFE'
#define CURLAUTH_ANYSAFE      (~(CURLAUTH_BASIC|CURLAUTH_DIGEST_IE))
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Curl.xs:1100:26: warning: implicit conversion from enumeration type 'C
+URLINFO' to different enumeration type 'CURLoption' [-Wenum-conversio
+n]
                curl_easy_setopt(easy, CURLINFO_PRIVATE, NULL);
                ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~
/usr/local/Cellar/curl/7.58.0/include/curl/curl.h:2744:68: note: expan
+ded from macro 'curl_easy_setopt'
#define curl_easy_setopt(handle,opt,param) curl_easy_setopt(handle,opt
+,param)
                                           ~~~~~~~~~~~~~~~~        ^~~
4 warnings generated.
rm -f blib/arch/auto/WWW/Curl/Curl.bundle
LD_RUN_PATH="/usr/local/Cellar/curl/7.58.0/lib:/usr/lib" env MACOSX_DE
+PLOYMENT_TARGET=10.3 cc  -bundle -undefined dynamic_lookup -L/usr/loc
+al/lib -fstack-protector-strong Curl.o  -o blib/arch/auto/WWW/Curl/Cu
+rl.bundle     \
       -L/usr/local/Cellar/curl/7.58.0/lib -lcurl -lldap -lz      \
      
ld: warning: object file (Curl.o) was built for newer OSX version (10.
+12) than being linked (10.4)
chmod 755 blib/arch/auto/WWW/Curl/Curl.bundle
"/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/bin/perl" "-Iin
+c" -MExtUtils::Command::MM -e 'cp_nonempty' -- Curl.bs blib/arch/auto
+/WWW/Curl/Curl.bs 644
Manifying 1 pod document
[ns3:~/src/WWW-Curl-4.17] administrator% sudo make install
Running Mkbootstrap for WWW::Curl ()
chmod 644 "Curl.bs"
Manifying 1 pod document
Files found in blib/arch: installing files in blib/lib into architectu
+re dependent library tree
Appending installation info to /Users/administrator/perl5/perlbrew/per
+ls/perl-5.24.0/lib/5.24.0/darwin-2level/perllocal.pod
[ns3:~/src/WWW-Curl-4.17] administrator%
[download]

(note: I reversed your earlier recommendation for the Curl.xs change, and am still able to compile without the CURL_DID_MEMORY_FUNC_TYPEDEFS error.)

Unfortunately as you can see, an old glitch in Makefile.PL seems to have come back to haunt me... I am getting a linking error in the make install that the Curl.o object file was built for a newer OS (10.12, the server OS) than being linked (10.4, which I guess is the lowest common denominator selected, or it could be due to my perl version, see below).


LD_RUN_PATH="/usr/local/Cellar/curl/7.58.0/lib:/usr/lib" env MACOSX_DE
+PLOYMENT_TARGET=10.3 cc  -bundle -undefined dynamic_lookup -L/usr/loc
+al/lib -fstack-protector-strong Curl.o  -o blib/arch/auto/WWW/Curl/Cu
+rl.bundle     \
       -L/usr/local/Cellar/curl/7.58.0/lib -lcurl -lldap -lz      \
      
ld: warning: object file (Curl.o) was built for newer OSX version (10.
+12) than being linked (10.4)
[download]

I believe this results from when I tripped over the error: unterminated conditional directive during my initial perl Makerfile.PL call:

/usr/include/AvailabilityInternal.h:22938:10: error: unterminated cond
+itional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_12
         ^
/usr/include/AvailabilityInternal.h:22867:10: error: unterminated cond
+itional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11_4
         ^
/usr/include/AvailabilityInternal.h:22800:10: error: unterminated cond
+itional directive
        #if __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_11_3
         ^
[download]

I guess I cannot ignore those error after all. From what I researched, the preprocessor is tripping over indented conditional if/ifndef/etc directives, likely due to its duties testing off-side languages like Python. I hear that using gcc instead can fix the problem, but I have no idea how to encourage Perl Makefile.PL to use gcc instead (which I do have installed).

I thought I might experiment by removing all the leading whitespace on each line of /usr/include/AvailabilityInternal.h , but boy, the OS will NOT let me change that file in any way. Not even via su or sudo.

Even the binary that I did manage to make install has problems running:

#! /usr/bin/perl
# linkrabbit.pl
use strict;
use warnings;

# use lib "/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/s
+ite_perl/5.24.0/darwin-2level/";
use lib "/Users/administrator/src/WWW-Curl-4.17/lib/";

use Time::Local;
use Time::HiRes;
use Getopt::Long;

use IO::Handle;
use HTML::TokeParser;
use XML::LibXML;
use WWW::RobotRules;
use LWP::Simple qw(get);
use URI;
use Switch;
use WWW::Curl::Easy;


[ns3:~/linkrabbit] administrator% ./linkrabbit.pl -s iq
Can't find 'boot_WWW__Curl' symbol in /usr/lib/libCurl.dylib
 at /Users/administrator/src/WWW-Curl-4.17/lib/WWW/Curl/Easy.pm line 9
+.
Compilation failed in require at /Users/administrator/src/WWW-Curl-4.1
+7/lib/WWW/Curl/Easy.pm line 9.
BEGIN failed--compilation aborted at /Users/administrator/src/WWW-Curl
+-4.17/lib/WWW/Curl/Easy.pm line 9.
Compilation failed in require at ./linkrabbit.pl line 38.
BEGIN failed--compilation aborted at ./linkrabbit.pl line 38.
Undefined subroutine &WWW::Curl::_global_cleanup called at /Users/admi
+nistrator/src/WWW-Curl-4.17/lib/WWW/Curl.pm line 11.
END failed--call queue aborted at ./linkrabbit.pl line 38.
[ns3:~/linkrabbit] administrator%
[download]

These exciting new errors definitely show progress... I am thinking it might be related to ancient 10.4 code running on 10.12. I am thinking I need to fix those OS X version tests in Makefile.PL.

I was able to eliminate the 2nd error (Undefined subroutine &WWW::Curl::_global_cleanup) simply by deleting the reference in Curl.pm, as I read it was not needed, but still cannot eliminate (or even find reference to) Can't find 'boot_WWW__Curl' symbol in /usr/lib/libCurl.dylib

FYI, I located the new code path, and forced it via the use lib directive above. The make install did not include it in per @inc (I should probably install it elsewhere, but where...? There seem to be multiple choices, will the real @INC please stand up):

[ns3:~] administrator% locate WWW/Curl/Easy
<snip>
/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.
+24.0/darwin-2level/WWW/Curl/Easy.pm
/Users/administrator/src/WWW-Curl-4.17/blib/lib/WWW/Curl/Easy.pm
/Users/administrator/src/WWW-Curl-4.17/lib/WWW/Curl/Easy.pm

[ns3:~] administrator% perl -e 'print join "\n", @INC, ""'
/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.
+24.0/darwin-2level
/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.
+24.0
/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/5.24.0/darwi
+n-2level
/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/5.24.0
.
[ns3:~] administrator%
[download]

I am confused why the 2 Easy.pm files (in /Users/administrator/src/WWW-Curl-4.17) are more up to date than the file supposedly installed with my make install (Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.24.0/darwin-2level/WWW/Curl.pm):

[ns3:~/src/WWW-Curl-4.17] administrator% sudo make install
Skip blib/lib/WWW/Curl/Easy.pm (unchanged)
cp lib/WWW/Curl.pm blib/lib/WWW/Curl.pm
Skip blib/lib/WWW/Curl/Share.pm (unchanged)
Skip blib/lib/WWW/Curl/Multi.pm (unchanged)
Skip blib/lib/WWW/Curl/Form.pm (unchanged)
Manifying 1 pod document
Files found in blib/arch: installing files in blib/lib into architectu
+re dependent library tree
Installing /Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/s
+ite_perl/5.24.0/darwin-2level/WWW/Curl.pm
Installing /Users/administrator/perl5/perlbrew/perls/perl-5.24.0/man/m
+an3/WWW::Curl.3
Appending installation info to /Users/administrator/perl5/perlbrew/per
+ls/perl-5.24.0/lib/5.24.0/darwin-2level/perllocal.pod
[ns3:~/src/WWW-Curl-4.17] administrator% 

[ns3:~/linkrabbit] administrator% ls /Users/administrator/perl5/perlbr
+ew/perls/perl-5.24.0/lib/site_perl/5.24.0/darwin-2level/WWW/Curl/Easy
+.pm /Users/administrator/src/WWW-Curl-4.17/blib/lib/WWW/Curl/Easy.pm 
+/Users/administrator/src/WWW-Curl-4.17/lib/WWW/Curl/Easy.pm
-r--r--r--  1 root           staff    18K 11 Feb 10:21 /Users/administ
+rator/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.24.0/darwin-2l
+evel/WWW/Curl/Easy.pm
-r--r--r--  1 administrator  staff    18K 11 Feb 12:06 /Users/administ
+rator/src/WWW-Curl-4.17/blib/lib/WWW/Curl/Easy.pm
-rw-r--r--  1 administrator  staff    18K 11 Feb 12:06 /Users/administ
+rator/src/WWW-Curl-4.17/lib/WWW/Curl/Easy.pm
[download]

My linkrabbit.pl code fails even worse if I point the use lib to /Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/site_perl/5.24.0/darwin-2level/

Maybe I am chasing wild geese. Perhaps the problem is with my perl itself? I checked to see that I am using my perlbrew instance:

[ns3:~/src/WWW-Curl-4.17] administrator% which perl
/Users/administrator/perl5/perlbrew/perls/perl-5.24.0/bin/perl
[download]

The linker and libraries did not seem encouraging: ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc'

[ns3:~/src/WWW-Curl-4.17] administrator% perl -V
Summary of my perl5 (revision 5 version 24 subversion 0) configuration
+:
   
  Platform:
    osname=darwin, osvers=14.5.0, archname=darwin-2level
    uname='darwin ns3.igods.com 14.5.0 darwin kernel version 14.5.0: s
+un sep 25 22:07:15 pdt 2016; root:xnu-2782.50.9~1release_x86_64 x86_6
+4 '
    config_args='-de -Dprefix=/Users/administrator/perl5/perlbrew/perl
+s/perl-5.24.0 -Aeval:scriptdir=/Users/administrator/perl5/perlbrew/pe
+rls/perl-5.24.0/bin'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-common -DPERL_DARWIN -fno-strict-aliasing 
+-pipe -fstack-protector-strong -I/usr/local/include -DPERL_USE_SAFE_P
+UTENV',
    optimize='-O3',
    cppflags='-fno-common -DPERL_DARWIN -fno-strict-aliasing -pipe -fs
+tack-protector-strong -I/usr/local/include'
    ccversion='', gccversion='4.2.1 Compatible Apple LLVM 7.0.2 (clang
+-700.1.81)', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
+, doublekind=3
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+6, longdblkind=3
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags =' -fstack-prot
+ector-strong -L/usr/local/lib'
    libpth=/Applications/Xcode.app/Contents/Developer/Toolchains/Xcode
+Default.xctoolchain/usr/bin/../lib/clang/7.0.2/lib /Applications/Xcod
+e.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib 
+/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/
+Developer/SDKs/MacOSX10.11.sdk/usr/lib /usr/local/lib /usr/lib
    libs=-lpthread -ldbm -ldl -lm -lutil -lc
    perllibs=-lpthread -ldl -lm -lutil -lc
    libc=, so=dylib, useshrplib=false, libperl=libperl.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
    cccdlflags=' ', lddlflags=' -bundle -undefined dynamic_lookup -L/u
+sr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options: HAS_TIMES PERLIO_LAYERS PERL_COPY_ON_WRITE
                        PERL_DONT_CREATE_GVSV
                        PERL_HASH_FUNC_ONE_AT_A_TIME_HARD PERL_MALLOC_
+WRAP
                        PERL_PRESERVE_IVUV PERL_USE_SAFE_PUTENV
                        USE_64_BIT_ALL USE_64_BIT_INT USE_LARGE_FILES
                        USE_LOCALE USE_LOCALE_COLLATE USE_LOCALE_CTYPE
                        USE_LOCALE_NUMERIC USE_LOCALE_TIME USE_PERLIO
                        USE_PERL_ATOF
  Locally applied patches:
    Devel::PatchPerl 1.38
  Built under darwin
  Compiled at Dec 19 2016 14:26:21
  %ENV:
    PERLBREW_HOME="/Users/administrator/.perlbrew"
    PERLBREW_MANPATH="/Users/administrator/perl5/perlbrew/perls/perl-5
+.24.0/man"
    PERLBREW_PATH="/Users/administrator/perl5/perlbrew/bin:/Users/admi
+nistrator/perl5/perlbrew/perls/perl-5.24.0/bin"
    PERLBREW_PERL="perl-5.24.0"
    PERLBREW_ROOT="/Users/administrator/perl5/perlbrew"
    PERLBREW_SHELLRC_VERSION="0.82"
    PERLBREW_VERSION="0.82"
  @INC:
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/site_per
+l/5.24.0/darwin-2level
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/site_per
+l/5.24.0
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/5.24.0/d
+arwin-2level
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.0/lib/5.24.0
    .
[ns3:~/src/WWW-Curl-4.17] administrator%
[download]

I installed the latest perl 5.24.3:

sudo perlbrew install perl-5.24.3
[download]

but see the same MACOSX_DEPLOYMENT_TARGET=10.3 cc:

[ns3:~/src/WWW-Curl-4.17] root# perlbrew list
 * perl-5.24.3                               (installed on Sun Feb 11 
+13:34:22 2018)
   perl-5.24.0                               (installed on Mon Dec 19 
+15:15:33 2016)
   system                (5.18.2)            (installed on Tue Feb  6 
+12:07:11 2018)

[ns3:~/src/WWW-Curl-4.17] root# perl -V
Summary of my perl5 (revision 5 version 24 subversion 3) configuration
+:
   
  Platform:
    osname=darwin, osvers=16.7.0, archname=darwin-thread-multi-2level
    uname='darwin ns3.igods.com 16.7.0 darwin kernel version 16.7.0: t
+hu jan 11 22:59:40 pst 2018; root:xnu-3789.73.8~1release_x86_64 x86_6
+4 '
    config_args='-de -Dprefix=/Users/administrator/perl5/perlbrew/perl
+s/perl-5.24.3 -Dusethreads -Aeval:scriptdir=/Users/administrator/perl
+5/perlbrew/perls/perl-5.24.3/bin'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-fno-common -DPERL_DARWIN -fno-strict-aliasing 
+-pipe -fstack-protector-strong -I/usr/local/include',
    optimize='-O3',
    cppflags='-fno-common -DPERL_DARWIN -fno-strict-aliasing -pipe -fs
+tack-protector-strong -I/usr/local/include'
    ccversion='', gccversion='4.2.1 Compatible Apple LLVM 9.0.0 (clang
+-900.0.39.2)', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
+, doublekind=3
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+6, longdblkind=3
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags =' -fstack-prot
+ector-strong -L/usr/local/lib'
    libpth=/usr/local/lib /Applications/Xcode.app/Contents/Developer/T
+oolchains/XcodeDefault.xctoolchain/usr/lib/clang/9.0.0/lib /Applicati
+ons/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/
+usr/lib /usr/lib
    libs=-lpthread -ldbm -ldl -lm -lutil -lc
    perllibs=-lpthread -ldl -lm -lutil -lc
    libc=, so=dylib, useshrplib=false, libperl=libperl.a
    gnulibc_version=''
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
    cccdlflags=' ', lddlflags=' -bundle -undefined dynamic_lookup -L/u
+sr/local/lib -fstack-protector-strong'


Characteristics of this binary (from libperl): 
  Compile-time options: HAS_TIMES MULTIPLICITY PERLIO_LAYERS
                        PERL_COPY_ON_WRITE PERL_DONT_CREATE_GVSV
                        PERL_HASH_FUNC_ONE_AT_A_TIME_HARD
                        PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP
                        PERL_PRESERVE_IVUV USE_64_BIT_ALL USE_64_BIT_I
+NT
                        USE_ITHREADS USE_LARGE_FILES USE_LOCALE
                        USE_LOCALE_COLLATE USE_LOCALE_CTYPE
                        USE_LOCALE_NUMERIC USE_LOCALE_TIME USE_PERLIO
                        USE_PERL_ATOF USE_REENTRANT_API
  Locally applied patches:
    Devel::PatchPerl 1.38
  Built under darwin
  Compiled at Feb 11 2018 13:17:46
  %ENV:
    PERL5LIB=""
    PERLBREW_LIB=""
    PERLBREW_MANPATH="/Users/administrator/perl5/perlbrew/perls/perl-5
+.24.3/man"
    PERLBREW_PATH="/Users/administrator/perl5/perlbrew/bin:/Users/admi
+nistrator/perl5/perlbrew/perls/perl-5.24.3/bin"
    PERLBREW_PERL="perl-5.24.3"
    PERLBREW_ROOT="/Users/administrator/perl5/perlbrew"
    PERLBREW_SKIP_INIT="1"
    PERLBREW_VERSION="0.78"
    PERL_LOCAL_LIB_ROOT=""
  @INC:
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.3/lib/site_per
+l/5.24.3/darwin-thread-multi-2level
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.3/lib/site_per
+l/5.24.3
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.3/lib/5.24.3/d
+arwin-thread-multi-2level
    /Users/administrator/perl5/perlbrew/perls/perl-5.24.3/lib/5.24.3
    .
[ns3:~/src/WWW-Curl-4.17] root#
[download]

I do not seem to be able to permanently switch my system over to 5.24.3 either, oddly... perlbrew switch runs exactly the same as perlbrew use, even when I sudo the command. That is an issue down the line, once I can get past my error: Can't find 'boot_WWW__Curl' symbol in /usr/lib/libCurl.dylib

[ns3:~/linkrabbit] root# ./linkrabbit.pl -s iq
Can't find 'boot_WWW__Curl' symbol in /usr/lib/libCurl.dylib
 at /Users/administrator/src/WWW-Curl-4.17/lib/WWW/Curl/Easy.pm line 9
+.
Compilation failed in require at /Users/administrator/src/WWW-Curl-4.1
+7/lib/WWW/Curl/Easy.pm line 9.
BEGIN failed--compilation aborted at /Users/administrator/src/WWW-Curl
+-4.17/lib/WWW/Curl/Easy.pm line 9.
Compilation failed in require at ./linkrabbit.pl line 38.
BEGIN failed--compilation aborted at ./linkrabbit.pl line 38.
[ns3:~/linkrabbit] root#
[download]

Running perl 5.24.0, I see WWW::Curl installed, but not WWW::Curl::Easy:

[ns3:~] administrator% perlbrew list-modules
Algorithm::Diff
App::cpanminus
CPAN
Config::Perl::V
File::HomeDir
File::Which
Mac::SystemDirectory
Perl
Spiffy
Test::Base
Test::Deep
Test::NoWarnings
Test::YAML
Text::Diff
WWW::Curl
YAML
install
[ns3:~] administrator%
[download]

Switching (only temporarily!!) to perl 5.24.3, I see no perl modules installed (as I would expect, since this install is so fresh and new):

[ns3:~] administrator% perlbrew switch perl-5.24.3
A sub-shell is launched with perl-5.24.3 as the activated perl. Run 'e
+xit' to finish it.
bash-3.2$ perlbrew list-modules
Perl
bash-3.2$
[download]

Yet, when I run my perl program, I get the same error:

bash-3.2$ ./linkrabbit.pl -s iq
Can't find 'boot_WWW__Curl' symbol in /usr/lib/libCurl.dylib
 at /Users/administrator/src/WWW-Curl-4.17/lib/WWW/Curl/Easy.pm line 9
+.
Compilation failed in require at /Users/administrator/src/WWW-Curl-4.1
+7/lib/WWW/Curl/Easy.pm line 9.
BEGIN failed--compilation aborted at /Users/administrator/src/WWW-Curl
+-4.17/lib/WWW/Curl/Easy.pm line 9.
Compilation failed in require at ./linkrabbit.pl line 38.
BEGIN failed--compilation aborted at ./linkrabbit.pl line 38.
[download]

This leads me to conclude that even though I did a make install, the module is not accessible perl. I only know how to do install modules via cpan (which failed, forcing me into this manual install). Am I missing something fundamental here?

This is one deep rabbit hole.

I guess I cannot ignore those error after all. From what I researched, the preprocessor is tripping over indented conditional if/ifndef/etc directives

Yes, my take on the stackoverflow post that I linked to earlier is that /usr/bin/cpp is doing the preprocessing, not gcc -E

I have no idea how to encourage Perl Makefile.PL to use gcc instead (which I do have installed)

Two ways that I know of:
1) for a manual build, perl Makefile.PL CC=gcc
2) with cpanm, cpanm WWW::Curl --configure-args="CC=gcc"
I haven't actually used the second method to pass CC=gcc to the build process, but I have used that to successfully pass other arguments.

However, I think you might strike issues with using gcc here, unless perl itself is built using gcc.

Can't find 'boot_WWW__Curl' symbol in /usr/lib/libCurl.dylib

This error is coming from perl. Doing a perlmonks supersearch for boot_ will throw up lots of posts, some of which should provide the solution (or at least an explanation).
Yell out if you need more help with any of that - though you seem to be making pretty good progress, anyway.

Cheers,
Rob