interactive/touch-events: Protect x11-specific calls

Use the CLUTTER_WINDOWING_X11 define to protect platform-specific calls
like clutter_x11_enable_xinput().

https://bugzilla.gnome.org/show_bug.cgi?id=678423

tests/interactive/test-touch-events.c

@@ -112,7 +112,9 @@ test_touch_events_main (int argc, char *argv[])
   ClutterActor *stage, *canvas;
   int i;
 
+#ifdef CLUTTER_WINDOWING_X11
   clutter_x11_enable_xinput ();
+#endif
 
   /* initialize Clutter */
   if (clutter_init (&argc, &argv) != CLUTTER_INIT_SUCCESS)