Under Unix wxDEBUG_LEVEL can be set using configure --enable-debug=max option
but under Windows it needs to be changed in wx/msw/setup.h so add it to this
file with a comment explaining its meaning.
Also document this symbol with the other preprocessor constants.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61890 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775