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/init.cpp

@@ -68,7 +68,7 @@ class wxDummyConsoleApp : public wxAppConsole
 public:
     wxDummyConsoleApp() { }
 
-    virtual int OnRun() { wxFAIL_MSG( wxT("unreachable code") ); return 0; }
+    virtual int OnRun() wxOVERRIDE { wxFAIL_MSG( wxT("unreachable code") ); return 0; }
     virtual bool DoYield(bool, long) { return true; }
 
     wxDECLARE_NO_COPY_CLASS(wxDummyConsoleApp);