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/generic/treectlg.cpp

@@ -80,7 +80,7 @@ public:
 
     wxTreeRenameTimer( wxGenericTreeCtrl *owner );
 
-    virtual void Notify();
+    virtual void Notify() wxOVERRIDE;
 
 private:
     wxGenericTreeCtrl *m_owner;
@@ -126,7 +126,7 @@ public:
 
     wxTreeFindTimer( wxGenericTreeCtrl *owner ) { m_owner = owner; }
 
-    virtual void Notify() { m_owner->ResetFindState(); }
+    virtual void Notify() wxOVERRIDE { m_owner->ResetFindState(); }
 
 private:
     wxGenericTreeCtrl *m_owner;