atomic: prefer gcc builtins over win32 atomics, if available.

The mingw win32 atomics appear to be faulty, so they should not be used
if the gcc ones are available.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/atomic.h

@@ -23,10 +23,10 @@
 
 #include "config.h"
 
-#if HAVE_MEMORYBARRIER
-#include "atomic_win32.h"
-#elif HAVE_SYNC_VAL_COMPARE_AND_SWAP
+#if HAVE_SYNC_VAL_COMPARE_AND_SWAP
 #include "atomic_gcc.h"
+#elif HAVE_MEMORYBARRIER
+#include "atomic_win32.h"
 #elif HAVE_MACHINE_RW_BARRIER
 #include "atomic_suncc.h"
 #else