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/image.cpp

@@ -3649,8 +3649,8 @@ class wxImageModule: public wxModule
 DECLARE_DYNAMIC_CLASS(wxImageModule)
 public:
     wxImageModule() {}
-    bool OnInit() { wxImage::InitStandardHandlers(); return true; }
-    void OnExit() { wxImage::CleanUpHandlers(); }
+    bool OnInit() wxOVERRIDE { wxImage::InitStandardHandlers(); return true; }
+    void OnExit() wxOVERRIDE { wxImage::CleanUpHandlers(); }
 };
 
 IMPLEMENT_DYNAMIC_CLASS(wxImageModule, wxModule)