build fix for GTK1 after r67299

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67368 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk1/window.h

@@ -10,6 +10,8 @@
 #ifndef __GTKWINDOWH__
 #define __GTKWINDOWH__
 
+typedef struct _GtkTooltips GtkTooltips;
+
 // helper structure that holds class that holds GtkIMContext object and
 // some additional data needed for key events processing
 struct wxGtkIMData;