I don't have a solution or workaround.

As you are compiling C or C++ components, I would avoid any xlocale.h path which is not available on (Cygwin or MinGW) system-wide basis; that includes all the Perl & Wx specific ones.

Per Cygwin Package search, the file is in "cygwin-devel-3.0.7-1" (your older version) and 3 "libc++-devel" Clang packages (but GCC is being used per your output). Seems like either LibXML::XML has be to be updated for this (possibly things have moved to "locale.h"; in which case replace all "xlocale" with "locale") or downgrade to 3.0.7 Cygwin. :-(

Try explicitly passing /usr/include and /usr/include/c++/v1/support/xlocale include paths to the compiler (may be possible via an environment variable or some option to make). As a test, try to manually compile Av_CharPtrPtr.c first ... 

>  cd <wherever LibXML::XML was being compiled>

#  Below "\" on 3 continuous lines is used as line continuation charac
+ter.
#  Escape|Quote as desired.
#
>  gcc -c  -I/usr/include/libxml2 -DPERL_USE_SAFE_PUTENV -U__STRICT_AN
+SI__ -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protect
+or-strong -D_FORTIFY_SOURCE=2 -DUSEIMPORTLIB -O3   -DVERSION=\"2.0206
+\" -DXS_VERSION=\"2.0206\"  \
-I/usr/include  \
-I/usr/include/c++/v1/support/xlocale  \
"-I/home/ken/perl5/perlbrew/perls/perl-5.32.0/lib/5.32.0/cygwin-thread
+-multi/CORE" -DHAVE_UTF8 Av_CharPtrPtr.c

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In reply to Re: Update XML::LibXML - can't find "xlocale.h" by parv
in thread Update XML::LibXML - can't find "xlocale.h" by kcott

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