Enable -DPERL_USE_SAFE_PUTENV in older versions of Perl on darwin.

[shogo82148]

-DPERL_USE_SAFE_PUTENV was removed in Perl 5.37.1, but it is still required for older versions of Perl on darwin.

Made the following changes to hints/darwin.sh:

--- hints/darwin.sh.old	2026-03-22 00:12:35
+++ hints/darwin.sh	2026-03-22 00:13:13
@@ -526,6 +526,26 @@
 # makefile in the same place.  Since Darwin uses GNU make, this dodges
 # the problem.
 firstmakefile=GNUmakefile;
+
+# >= 5.23.6 and <= 5.37.0 have a problem with setenv() in atfork handlers on Darwin,
+# so enable -DPERL_USE_SAFE_PUTENV, ref. https://github.com/Perl/perl5/commit/e3962106e93fa80bf960e71ac7c7727e7e15eee8
+# This behavior became the default after version 5.37.0, ref. https://github.com/Perl/perl5/commit/ae6b6b71cdbfb3fb6e1192178fa1e530a2f07ece
+if [ "$perl_revision" -eq 5 ] && \
+   { [ "$perl_version" -gt 23 ] || \
+     { [ "$perl_version" -eq 23 ] && [ "$perl_subversion" -ge 6 ]; }; } && \
+   { [ "$perl_version" -lt 37 ] || \
+     { [ "$perl_version" -eq 37 ] && [ "$perl_subversion" -le 0 ]; }; }
+then
+  # Parts of the system call setenv(), in particular in an atfork handler.
+  # This causes problems when the child tries to clean up environ[], so
+  # let libc manage environ[].
+  cat >> config.over <<'EOOVER'
+if test "$d_unsetenv" = "$define" -a \
+    `expr "$ccflags" : '.*-DPERL_USE_SAFE_PUTENV'` -eq 0; then
+        ccflags="$ccflags -DPERL_USE_SAFE_PUTENV"
+fi
+EOOVER
+fi

 # if you use a newer toolchain before OS X 10.9 these functions may be
 # incorrectly detected, so disable them

fixes #68