Absorb -D_USE_32BIT_TIME_T switch from Perl, if relevant.

Commit 3c163a7fc's original choice to ignore all #define symbols whose
names begin with underscore turns out to be too simplistic.  On Windows,
some Perl installations are built with -D_USE_32BIT_TIME_T, and we must
absorb that or we get the wrong result for sizeof(PerlInterpreter).

This effectively re-reverts commit ef58b87df, which injected that symbol
in a hacky way, making it apply to all of Postgres not just PL/Perl.
More significantly, it did so on *all* 32-bit Windows builds, even when
the Perl build to be used did not select this option; so that it fails
to work properly with some newer Perl builds.

By making this change, we would be introducing an ABI break in 32-bit
Windows builds; but fortunately we have not used type time_t in any
exported Postgres APIs in a long time.  So it should be OK, both for
PL/Perl itself and for third-party extensions, if an extension library
is built with a different _USE_32BIT_TIME_T setting than the core code.

Patch by me, based on research by Ashutosh Sharma and Robert Haas.
Back-patch to all supported branches, as commit 3c163a7fc was.

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

src/tools/msvc/MSBuildProject.pm

@@ -63,21 +63,16 @@ EOF
   </PropertyGroup>
 EOF
 
-	# We have to use this flag on 32 bit targets because the 32bit perls
-	# are built with it and sometimes crash if we don't.
-	my $use_32bit_time_t =
-	  $self->{platform} eq 'Win32' ? '_USE_32BIT_TIME_T;' : '';
-
 	$self->WriteItemDefinitionGroup(
 		$f, 'Debug',
-		{   defs    => "_DEBUG;DEBUG=1;$use_32bit_time_t",
+		{   defs    => "_DEBUG;DEBUG=1",
 			opt     => 'Disabled',
 			strpool => 'false',
 			runtime => 'MultiThreadedDebugDLL' });
 	$self->WriteItemDefinitionGroup(
 		$f,
 		'Release',
-		{   defs    => "$use_32bit_time_t",
+		{   defs    => "",
 			opt     => 'Full',
 			strpool => 'true',
 			runtime => 'MultiThreadedDLL' });