Further tweaks to compiler flags for PL/Perl on Windows.

It now emerges that we can only rely on Perl to tell us we must use
-D_USE_32BIT_TIME_T if it's Perl 5.13.4 or later.  For older versions,
revert to our previous practice of assuming we need that symbol in
all 32-bit Windows builds.  This is not ideal, but inquiring into
which compiler version Perl was built with seems far too fragile.
In any case, we had not previously had complaints about these old
Perl versions, so let's assume this is Good Enough.  (It's still
better than the situation ante commit 5a5c2fec, in that at least
the effects are confined to PL/Perl rather than the whole PG build.)

Back-patch to all supported versions, like 5a5c2fec and predecessors.

Discussion: https://postgr.es/m/CANFyU97OVQ3+Mzfmt3MhuUm5NwPU=-FtbNH5Eb7nZL9ua8=rcA@mail.gmail.com

src/tools/msvc/Mkvcbuild.pm

@@ -530,6 +530,18 @@ sub mkvcbuild
 			}
 		}
 
+		# Perl versions before 5.13.4 don't provide -D_USE_32BIT_TIME_T
+		# regardless of how they were built.  On 32-bit Windows, assume
+		# such a version was built with a pre-MSVC-2005 compiler, and
+		# define the symbol anyway, so that we are compatible if we're
+		# being built with a later MSVC version.
+		push(@perl_embed_ccflags, '_USE_32BIT_TIME_T')
+		  if $solution->{platform} eq 'Win32'
+			  && $Config{PERL_REVISION} == 5
+			  && ($Config{PERL_VERSION} < 13
+				  || (   $Config{PERL_VERSION} == 13
+					  && $Config{PERL_SUBVERSION} < 4));
+
 		# Also, a hack to prevent duplicate definitions of uid_t/gid_t
 		push(@perl_embed_ccflags, 'PLPERL_HAVE_UID_GID');