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/xrc/xmlres.cpp

@@ -1386,7 +1386,7 @@ class wxXmlSubclassFactoryCXX : public wxXmlSubclassFactory
 public:
     ~wxXmlSubclassFactoryCXX() {}
 
-    wxObject *Create(const wxString& className)
+    wxObject *Create(const wxString& className) wxOVERRIDE
     {
         wxClassInfo* classInfo = wxClassInfo::FindClass(className);
 
@@ -2859,12 +2859,12 @@ class wxXmlResourceModule: public wxModule
 DECLARE_DYNAMIC_CLASS(wxXmlResourceModule)
 public:
     wxXmlResourceModule() {}
-    bool OnInit()
+    bool OnInit() wxOVERRIDE
     {
         wxXmlResource::AddSubclassFactory(new wxXmlSubclassFactoryCXX);
         return true;
     }
-    void OnExit()
+    void OnExit() wxOVERRIDE
     {
         delete wxXmlResource::Set(NULL);
         delete wxIdRangeManager::Set(NULL);