Add wxApp::GTKIsUsingGlobalMenu() helper to wxGTK.

This allows to check whether the global menu is being used and will be mostly
useful for working around various bugs/problems uncovered by it.

See #14302.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73008 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/app.h

@@ -56,6 +56,13 @@ public:
     // must return XVisualInfo pointer (it is not freed by caller)
     virtual void *GetXVisualInfo() { return NULL; }
 
+    // Check if we're using a global menu. Currently this is only true when
+    // running under Ubuntu Unity and global menu is not disabled.
+    //
+    // This is mostly used in the implementation in order to work around
+    // various bugs arising due to this.
+    static bool GTKIsUsingGlobalMenu();
+
 #if wxUSE_LIBHILDON || wxUSE_LIBHILDON2
     // Maemo-specific method: get the main program object
     HildonProgram *GetHildonProgram();