Compilation fix for wxGUIEventLoop in wxDFB

Rename YieldFor() to DoYieldFor() in the header too.

This was broken by f740cc3881

include/wx/dfb/evtloop.h

@@ -24,11 +24,12 @@ class WXDLLIMPEXP_CORE wxGUIEventLoop : public wxConsoleEventLoop
 public:
     wxGUIEventLoop();
 
-    virtual bool YieldFor(long eventsToProcess);
-
     // returns DirectFB event buffer used by wx
     static wxIDirectFBEventBufferPtr GetDirectFBEventBuffer();
 
+protected:
+    virtual void DoYieldFor(long eventsToProcess);
+
 private:
     static void InitBuffer();
     static void CleanUp();