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/stattextcmn.cpp

@@ -169,12 +169,12 @@ public:
     }
 
 protected:
-    virtual void OnOutputLine(const wxString& line)
+    virtual void OnOutputLine(const wxString& line) wxOVERRIDE
     {
         m_text += line;
     }
 
-    virtual void OnNewLine()
+    virtual void OnNewLine() wxOVERRIDE
     {
         m_text += wxT('\n');
     }