Add some missing definitions for mingw.org

these shouldn't be necessary if _WIN32_WINNT >= _WIN32_WINNT_VISTA

src/win32/mingw-compat.h

@@ -17,6 +17,13 @@
 #define stat _stati64
 #endif
 
+#if _WIN32_WINNT < 0x0600 && !defined(__MINGW64_VERSION_MAJOR)
+#undef MemoryBarrier
+void __mingworg_MemoryBarrier(void);
+#define MemoryBarrier __mingworg_MemoryBarrier
+#define VOLUME_NAME_DOS 0x0
+#endif
+
 #endif
 
 #endif /* INCLUDE_mingw_compat__ */