use wxOVERRIDE in wxMSW sources

src/msw/thread.cpp

@@ -1207,8 +1207,8 @@ bool wxThread::TestDestroy()
 class wxThreadModule : public wxModule
 {
 public:
-    virtual bool OnInit();
-    virtual void OnExit();
+    virtual bool OnInit() wxOVERRIDE;
+    virtual void OnExit() wxOVERRIDE;
 
 private:
     wxDECLARE_DYNAMIC_CLASS(wxThreadModule);