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/intl.cpp

@@ -1802,12 +1802,12 @@ class wxLocaleModule: public wxModule
     public:
         wxLocaleModule() {}
 
-        bool OnInit()
+        bool OnInit() wxOVERRIDE
         {
             return true;
         }
 
-        void OnExit()
+        void OnExit() wxOVERRIDE
         {
             wxLocale::DestroyLanguagesDB();
         }