Turn off deprecated bison warnings under MSVC

These are disabled by the configure code, so this is just fixing an
inconsistency in the MSVC code.

Backpatch to all live branches.

src/tools/msvc/pgbison.pl

@@ -45,5 +45,7 @@ close($mf);
 my $basetarg = basename($output);
 my $headerflag = ($make =~ /^$basetarg:\s+BISONFLAGS\b.*-d/m ? '-d' : '');
 
-system("bison $headerflag $input -o $output");
+my $nodep = $bisonver ge '3.0' ? "-Wno-deprecated" : "";
+
+system("bison $nodep $headerflag $input -o $output");
 exit $? >> 8;