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

utils/wxrc/wxrc.cpp

@@ -223,8 +223,8 @@ class XmlResApp : public wxAppConsole
 {
 public:
     // don't use builtin cmd line parsing:
-    virtual bool OnInit() { return true; }
-    virtual int OnRun();
+    virtual bool OnInit() wxOVERRIDE { return true; }
+    virtual int OnRun() wxOVERRIDE;
 
 private:
     void ParseParams(const wxCmdLineParser& cmdline);