Compilation fix in non-PCH build of wxMSW wxStaticBox.

Include wx/sizer.h now that we use sizers in static box DoGetBestSize().

Closes #14397.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71725 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/statbox.cpp

@@ -33,6 +33,7 @@
     #include "wx/dcclient.h"
     #include "wx/dcmemory.h"
     #include "wx/image.h"
+    #include "wx/sizer.h"
 #endif
 
 #include "wx/notebook.h"