Add wxOVERRIDE and use it in common and wxOSX code.

Make overriding virtual methods more explicit and enable additional checks
provided by C++11 compilers when "override" is used.

Closes #16100.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76173 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/dcbase.cpp

@@ -117,8 +117,8 @@ wxDCFactory *wxDCFactory::Get()
 class wxDCFactoryCleanupModule : public wxModule
 {
 public:
-    virtual bool OnInit() { return true; }
-    virtual void OnExit() { wxDCFactory::Set(NULL); }
+    virtual bool OnInit() wxOVERRIDE { return true; }
+    virtual void OnExit() wxOVERRIDE { wxDCFactory::Set(NULL); }
 
 private:
     DECLARE_DYNAMIC_CLASS(wxDCFactoryCleanupModule)