Don't call ::GetLayout() in wxMSW code directly.

Use wxMSW::GetLayout() wrapper to avoid directly binding to a function not
present in old Windows versions and also to fix linking errors with MinGW
after the changes of r73484.

See #3995.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@73488 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775