Fixed WinRT build.

include/bx/cpu.h

@@ -19,6 +19,9 @@
 #		include <intrin.h>
 #		include <windows.h>
 #	endif // !BX_PLATFORM_XBOX360
+#	if BX_PLATFORM_WINRT
+#		define _InterlockedExchangeAdd64 InterlockedExchangeAdd64
+#	endif // BX_PLATFORM_WINRT
 extern "C" void _ReadBarrier();
 extern "C" void _WriteBarrier();
 extern "C" void _ReadWriteBarrier();