Codechange: Use EnumBitSet for WindowDefaultFlags.

src/build_vehicle_gui.cpp

@@ -1921,7 +1921,7 @@ struct BuildVehicleWindow : Window {
 static WindowDesc _build_vehicle_desc(
 	WDP_AUTO, "build_vehicle", 240, 268,
 	WC_BUILD_VEHICLE, WC_NONE,
-	WDF_CONSTRUCTION,
+	WindowDefaultFlag::Construction,
 	_nested_build_vehicle_widgets,
 	&BuildVehicleWindow::hotkeys
 );