Compilation fix after ownerdraw-refactor branch merge.

Don't use HDC in public headers, it may not be declared there. Use WXHDC
instead even if this means having ugly casts.

This fixed mingw32 compilation (see #11595).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63252 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/menuitem.h

@@ -120,7 +120,7 @@ protected:
 
 private:
     // helper function for draw std menu check mark
-    void DrawStdCheckMark(HDC hdc, const RECT* rc, wxODStatus stat);
+    void DrawStdCheckMark(WXHDC hdc, const RECT* rc, wxODStatus stat);
 
 #endif // wxUSE_OWNER_DRAWN