Document that wxOS_UNIX, wxOS_MAC and wxOS_WINDOWS enum values are combinations of other values (unfortunately doxygen does not show the definition of those symbols in the HTML docs so we need to explicitely state that). git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63650 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775