Detect 64bit builds using proper macros

Include/Rocket/Core/Platform.h

@@ -48,7 +48,7 @@
 	#define ROCKET_DEBUG
 #endif
 
-#if defined __x86_64__ || defined _M_X64 || defined __powerpc64__ || defined __alpha__ || defined __ia64__ || defined __s390__ || defined __s390x__
+#if defined __LP64__ || defined _M_X64 || defined __MING64__
     #define ROCKET_ARCH_64
 #else
     #define ROCKET_ARCH_32