Add a destroy_signal on weston_output
diff --git a/src/compositor.h b/src/compositor.h
index eb8ad82..3b08f29 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -175,6 +175,7 @@
 	struct weston_output_zoom zoom;
 	int dirty;
 	struct wl_signal frame_signal;
+	struct wl_signal destroy_signal;
 	uint32_t frame_time;
 	int disable_planes;