notify/osx_notifications: Fix build

We need to ignore the unguarded-availability diagnostic, we are already
using partial-availability here anyway.

modules/notify/osx_notifications.m

@@ -60,6 +60,8 @@
  * Preamble
  *****************************************************************************/
 
+#pragma clang diagnostic ignored "-Wunguarded-availability"
+
 #ifdef HAVE_CONFIG_H
 # include "config.h"
 #endif