Add an empty implementation of the OSXGenerateEvent() pure virtual so the generic date picker ctrl can be used in the cocoa build.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70536 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/datectrl.h

@@ -82,6 +82,10 @@ private:
     void OnSize(wxSizeEvent& event);
     void OnFocus(wxFocusEvent& event);
 
+#ifdef __WXOSX_COCOA__
+    virtual void OSXGenerateEvent(const wxDateTime& dt) {}
+#endif
+
     wxComboCtrl* m_combo;
     wxCalendarComboPopup* m_popup;