sync code with last improvements from OpenBSD

dist/fontconfig/meson-cc-tests/intel-atomic-primitives-test.c

@@ -0,0 +1,6 @@
+void memory_barrier (void) { __sync_synchronize (); }
+int atomic_add (int *i) { return __sync_fetch_and_add (i, 1); }
+int mutex_trylock (int *m) { return __sync_lock_test_and_set (m, 1); }
+void mutex_unlock (int *m) { __sync_lock_release (m); }
+
+int main(void) { return 0;}