fix wxClientDisplayRect() when wxUSE_DISPLAY==0

GDK_WINDOWING_X11 was not getting defined, causing hard coded size to be used


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76348 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/unix/displayx11.cpp

@@ -381,6 +381,9 @@ bool wxDisplayImplX11::ChangeMode(const wxVideoMode& WXUNUSED(mode))
 #endif /* wxUSE_DISPLAY */
 
 #include "wx/utils.h"
+#ifdef __WXGTK20__
+    #include <gdk/gdk.h>  // for GDK_WINDOWING_X11
+#endif
 
 #if wxUSE_LIBHILDON || wxUSE_LIBHILDON2 || !defined(GDK_WINDOWING_X11)