Annotate fallthrough when possible

Author: jserv

src/box.c

@@ -167,7 +167,7 @@ twin_dispatch_result_t _twin_box_dispatch(twin_widget_t *widget,
             _twin_box_xy_to_widget(box, event->u.pointer.x, event->u.pointer.y);
         if (box->button_down && box->button_down->want_focus)
             box->focus = box->button_down;
-    /* fall through ... */
+        fallthrough;
     case TwinEventButtonUp:
     case TwinEventMotion:
         if (box->button_down) {

src/convolve.c

@@ -162,7 +162,7 @@ static void _twin_subpath_convolve(twin_path_t *path,
             break;
         case TwinCapButt:
             p = ptarget - 1;
-            /* fall through … */
+            fallthrough;
         case TwinCapRound:
             while (p != ptarget) {
                 if (++p == np)