clang defines the macro that we use to test for GCC's extension support
for C11 atomics, but doesn't define the extension in the same way.
Check for clang and disable the macros again if we find it.
https://bugzilla.gnome.org/show_bug.cgi?id=731513
#if defined(G_ATOMIC_LOCK_FREE) && defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
/* We prefer the new C11-style atomic extension of GCC if available */
-#if defined(__ATOMIC_SEQ_CST)
+#if defined(__ATOMIC_SEQ_CST) && !defined(__clang__)
#define g_atomic_int_get(atomic) \
(G_GNUC_EXTENSION ({ \