Allow building wxGTK3 with Broadway backend.

Use GDK_WINDOWING_BROADWAY to fix compilation with it.

Closes #14469.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72075 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/window.cpp

@@ -2143,7 +2143,7 @@ wxWindow *wxGetActiveWindow()
 
 // Under Unix this is implemented using X11 functions in utilsx11.cpp but we
 // need to have this function under Windows too, so provide at least a stub.
-#ifdef __WINDOWS__
+#ifndef GDK_WINDOWING_X11
 bool wxGetKeyState(wxKeyCode WXUNUSED(key))
 {
     wxFAIL_MSG(wxS("Not implemented under Windows"));