Switch "cl /?" to "cl /help" in MSVC scripts for platform detection

"cl /?" produces a different output if run on a real or a virtual drive
(this can be set with a simple subst command), causing an error in the
MSVC scripts if building on a virtual drive because the platform to use
cannot be detected.

"cl /help", on the contrary, produces a consistent output if used on a
real or virtual drive.  Changing to "/help" allows the compilation to
work with a virtual drive as long as the top of the code repository is
part of the drive, without impacting the build on real drives.

Reported-by: Robert Grange
Author: Juan José Santamaría Flecha
Discussion: https://postgr.es/m/16825-c4f104bcebc67034@postgresql.org

src/tools/msvc/Solution.pm

@@ -62,7 +62,7 @@ sub DeterminePlatform
 	if ($^O eq "MSWin32")
 	{
 		# Examine CL help output to determine if we are in 32 or 64-bit mode.
-		my $output = `cl /? 2>&1`;
+		my $output = `cl /help 2>&1`;
 		$? >> 8 == 0 or die "cl command not found";
 		$self->{platform} =
 		  ($output =~ /^\/favor:<.+AMD64/m) ? 'x64' : 'Win32';