Use _WIN32_WINNT as value for BX_PLATFORM_WINDOWS macro.

include/bx/platform.h

@@ -51,7 +51,13 @@
 #	define BX_PLATFORM_XBOX360 1
 #elif defined(_WIN32) || defined(_WIN64)
 #	undef BX_PLATFORM_WINDOWS
-#	define BX_PLATFORM_WINDOWS 1
+// http://msdn.microsoft.com/en-us/library/6sehtctf.aspx
+#	if !defined(WINVER) && !defined(_WIN32_WINNT)
+// Windows Server 2003 with SP1, Windows XP with SP2 and above
+#		define WINVER 0x0502
+#		define _WIN32_WINNT 0x0502
+#	endif // !defined(WINVER) && !defined(_WIN32_WINNT)
+#	define BX_PLATFORM_WINDOWS _WIN32_WINNT
 #elif defined(__native_client__)
 // NaCl compiler defines __linux__
 #	undef BX_PLATFORM_NACL
@@ -145,13 +151,4 @@
 typedef struct { long double x, y; } __float128;
 #endif // BX_COMPILER_CLANG && BX_PLATFORM_LINUX
 
-#if BX_PLATFORM_WINDOWS
-// http://msdn.microsoft.com/en-us/library/6sehtctf.aspx
-#	if !defined(WINVER) && !defined(_WIN32_WINNT)
-		// Windows Server 2003 with SP1, Windows XP with SP2 and above
-#		define WINVER 0x0502
-#		define _WIN32_WINNT 0x0502
-#	endif // !defined(WINVER) && !defined(_WIN32_WINNT)
-#endif // BX_PLATFORM_WINDOWS
-
 #endif // __BX_PLATFORM_H__