Readd a return which was removed as dead code a while ago. icc may

* glib/gmain.c (child_watch_helper_thread): Readd a
        return which was removed as dead code a while ago.
        icc may consider it dead, but gcc doesn't like non-void
        functions without a return...  (#354707)

glib/gmain.c

@@ -3865,6 +3865,8 @@ child_watch_helper_thread (gpointer data)
 	}
       G_UNLOCK (main_context_list);
     }
+
+  return NULL;
 }
 
 static void