vkd3d: Only use __builtin_popcount in PE builds.

It's not compatible with -mabi=ms.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=52664
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

libs/vkd3d/include/private/vkd3d_common.h

@@ -65,7 +65,7 @@ static inline unsigned int vkd3d_popcount(unsigned int v)
 {
 #ifdef _MSC_VER
     return __popcnt(v);
-#elif defined(__GNUC__) && (__GNUC__ >= 4)
+#elif defined(__MINGW32__)
     return __builtin_popcount(v);
 #else
     v -= (v >> 1) & 0x55555555;