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/html/htmlwin.cpp

@@ -66,7 +66,7 @@ public:
         m_orient = orient;
     }
 
-    virtual void Notify();
+    virtual void Notify() wxOVERRIDE;
 
 private:
     wxScrolledWindow *m_win;
@@ -1846,8 +1846,8 @@ class wxHtmlWinModule: public wxModule
 DECLARE_DYNAMIC_CLASS(wxHtmlWinModule)
 public:
     wxHtmlWinModule() : wxModule() {}
-    bool OnInit() { return true; }
-    void OnExit() { wxHtmlWindow::CleanUpStatics(); }
+    bool OnInit() wxOVERRIDE { return true; }
+    void OnExit() wxOVERRIDE { wxHtmlWindow::CleanUpStatics(); }
 };
 
 IMPLEMENT_DYNAMIC_CLASS(wxHtmlWinModule, wxModule)