Replace a few __WXMSW__ tests with __WINDOWS__ as the former is not
defined any longer (since r73290) when compiling with wxUSE_GUI set to 0.
Tested changes with both wxGTK and wxMSW builds under Cygwin.
Closes#14382.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76759 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775