selectgen.ml: cross-cutting handling of Proc.contains_calls

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14609 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02
on i386 and AMD64, mark 'morally tail' C function calls as non-leaf

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@14610 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02