loader: Fix G overflowing for G(4) on 32-bit builds

Prevent G(4) and over from overflowing for 32-bit builds.

Reviewed by: imp
Pull Request: freebsd/freebsd-src#1098

stand/efi/loader/copy.c

@@ -36,7 +36,7 @@
 #include "loader_efi.h"
 
 #define	M(x)	((x) * 1024 * 1024)
-#define	G(x)	(1UL * (x) * 1024 * 1024 * 1024)
+#define	G(x)	(1ULL * (x) * 1024 * 1024 * 1024)
 
 #if defined(__amd64__)
 #include <machine/cpufunc.h>