Being the user the OP was talking about, let me drop into this discussion.

The error appears on the standard ActiveState distribution of Perl, both 5.8.8 and 5.10. The compiler flags, as shown by perl -V, are: 

    cc='cl', ccflags ='-nologo -GF -W3 -MD -Zi -DNDEBUG -O1 -DWIN32 -D
+_CONSOLE -DNO_STRICT -DHAVE_DES_FCRYPT -DNO_HASH_SEED -DUSE_SITECUSTO
+MIZE -DPRIVLIB_LAST_IN_INC -DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SY
+S -DUSE_PERLIO -DPERL_MSVCRT_READFIX',
    optimize='-MD -Zi -DNDEBUG -O1',
    cppflags='-DWIN32'
    ccversion='12.00.8804', gccversion='', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=undef, longlongsize=8, d_longdbl=define, longdblsize=8
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='__int64
+', lseeksize=8
    alignbytes=8, prototype=define

[download]
Update: Maybe this part of perl -V is also important: 
  Compile-time options: MULTIPLICITY PERL_IMPLICIT_CONTEXT
                        PERL_IMPLICIT_SYS PERL_MALLOC_WRAP
                        PL_OP_SLAB_ALLOC USE_ITHREADS USE_LARGE_FILES
                        USE_PERLIO USE_SITECUSTOMIZE

[download]
 But can we see from this whether it was compiled with fcntl.h?

Some other Fcntl macros work well - for instance, O_CREAT.

Even if O_NONBLOCK is not defined, I wonder why the error message is issued on a line, where only the existence is tested, i.e. 

if(exists $Fcntl::{'O_NONBLOCK')) { ... }

[download]
-- 
Ronald Fischer <ynnor@mm.st>

In reply to Re^2: Fcntl constants missing by rovf
in thread Fcntl constants missing by nwetters

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