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/html/m_hline.cpp

@@ -37,8 +37,8 @@ class wxHtmlLineCell : public wxHtmlCell
     public:
         wxHtmlLineCell(int size, bool shading) : wxHtmlCell() {m_Height = size; m_HasShading = shading;}
         void Draw(wxDC& dc, int x, int y, int view_y1, int view_y2,
-                  wxHtmlRenderingInfo& info);
-        void Layout(int w)
+                  wxHtmlRenderingInfo& info) wxOVERRIDE;
+        void Layout(int w) wxOVERRIDE
             { m_Width = w; wxHtmlCell::Layout(w); }
 
     private: