Use __WINDOWS__ for OS checks and __WXMSW__ for GUI checks (round 2).

This is continuation of r70796 and serves the same purpose.

Closes #14065, #14066.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70808 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

tests/strings/vararg.cpp

@@ -272,7 +272,7 @@ void VarArgTestCase::ArgsValidation()
 
     // check size_t handling
     size_t len = sizeof(*this);
-#ifdef __WXMSW__
+#ifdef __WINDOWS__
     wxString::Format("%Iu", len);
 #else
     wxString::Format("%zu", len);