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/hidjoystick.cpp

@@ -77,7 +77,7 @@ public:
     virtual ~wxHIDJoystick();
 
     bool Create(int nWhich);
-    virtual void BuildCookies(CFArrayRef Array);
+    virtual void BuildCookies(CFArrayRef Array) wxOVERRIDE;
     void MakeCookies(CFArrayRef Array);
     IOHIDElementCookie* GetCookies();
     IOHIDQueueInterface** GetQueue();
@@ -95,7 +95,7 @@ class wxJoystickThread : public wxThread
 {
 public:
     wxJoystickThread(wxHIDJoystick* hid, int joystick);
-    void* Entry();
+    void* Entry() wxOVERRIDE;
     static void HIDCallback(void* target, IOReturn res, void* context, void* sender);
 
 private: