(previously, you could end up with different ones depending on include
order, now platform.h is always (implicitly) included first, so
__WXMSW__ is guaranteed to be defined even in wxBase/MSW builds.)
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@19212 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775