PR#5921 "compact unwind" warnings under MacOS

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13423 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
added more stuff

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13424 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
fix wrong error message

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13425 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02