Enable the use of __sync_fetch_and_add().

Index: common/osdep.h
--- common/osdep.h.orig
+++ common/osdep.h
@@ -434,7 +434,7 @@ X264_API int x264_threading_init( void );
 static ALWAYS_INLINE int x264_pthread_fetch_and_add( int *val, int add, x264_pthread_mutex_t *mutex )
 {
 #if HAVE_THREAD
-#if defined(__GNUC__) && (__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ > 0) && (ARCH_X86 || ARCH_X86_64)
+#if defined(__GNUC__) && (__GNUC__ > 4 || __GNUC__ == 4 && __GNUC_MINOR__ > 0)
     return __sync_fetch_and_add( val, add );
 #else
     x264_pthread_mutex_lock( mutex );