Add note about CFI support for OS X.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13230 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
[arm] Add CFI directives to the native runtime.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13231 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02