Add gcc implementation for atomic ops
diff --git a/src/hb-atomic-private.hh b/src/hb-atomic-private.hh
index d6bd1c9..29e4146 100644
--- a/src/hb-atomic-private.hh
+++ b/src/hb-atomic-private.hh
@@ -56,10 +56,15 @@
#define hb_atomic_int_add(AI, V) (OSAtomicAdd32Barrier ((V), &(AI)) - (V))
+#elif !defined(HB_NO_MT) && defined(__GNUC__)
+
+typedef int hb_atomic_int_t;
+#define hb_atomic_int_add(AI, V) __sync_fetch_and_add (&(AI), (V))
+
#elif !defined(HB_NO_MT) && defined(HAVE_GLIB)
#include <glib.h>
-typedef volatile int hb_atomic_int_t;
+typedef int hb_atomic_int_t;
#if GLIB_CHECK_VERSION(2,29,5)
#define hb_atomic_int_add(AI, V) g_atomic_int_add (&(AI), (V))
#else
@@ -70,7 +75,7 @@
#else
#define HB_ATOMIC_INT_NIL 1
-typedef volatile int hb_atomic_int_t;
+typedef int hb_atomic_int_t;
#define hb_atomic_int_add(AI, V) (((AI) += (V)) - (V))
#endif
