PR#5976: crash after recovering from two stack overflows (ocamlopt on MacOS X)

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13759 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
PR#5976 continued: don't activate RETURN_AFTER_STACK_OVERFLOW yet on i386/macosx, as it needs testing on this platform

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13760 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02