Fix warnings: re-add enum forward declaration

src/video/wayland/SDL_waylanddyn.h

@@ -42,6 +42,9 @@ struct libdecor_state;
 struct libdecor_configuration;
 struct libdecor_interface;
 struct libdecor_frame_interface;
+enum libdecor_resize_edge;
+enum libdecor_capabilities;
+enum libdecor_window_state;
 
 #include <stdint.h>
 #include "wayland-cursor.h"