Cast the return value of g_array_free to void* before casting to char**

Let the compiler know that we don't want to use it as char*, so there is
no alignment error.

https://bugzilla.gnome.org/show_bug.cgi?id=760350
https://bugzilla.gnome.org/show_bug.cgi?id=755659

gtk/gtkactionmuxer.c

@@ -138,7 +138,7 @@ gtk_action_muxer_list_actions (GActionGroup *action_group)
                             actions);
     }
 
-  return (gchar **) g_array_free (actions, FALSE);
+  return (gchar **)(void *) g_array_free (actions, FALSE);
 }
 
 static Group *