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/osx/core/bitmap.cpp

@@ -66,7 +66,7 @@ public:
 
     virtual ~wxBitmapRefData();
 
-    virtual bool IsOk() const { return m_ok; }
+    virtual bool IsOk() const wxOVERRIDE { return m_ok; }
 
     void Free();
     void SetOk( bool isOk) { m_ok = isOk; }
@@ -1828,7 +1828,7 @@ public:
                           const wxString& name,
                           wxBitmapType type,
                           int desiredWidth,
-                          int desiredHeight);
+                          int desiredHeight) wxOVERRIDE;
 };
 
 IMPLEMENT_ABSTRACT_CLASS(wxBundleResourceHandler, wxBitmapHandler);