This fixes compilation of non-wxOSX ports (e.g. wxGTK) under OS X.
Also make the difference between the two symbols more clear in the
documentation.
Closes#14503.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72180 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775