Add __stack_chk_fail to mini-os and __sprintf_chk __fprintf_chk to
newlib, to cope with ocaml runtimes compiled with -fstack-protector.
From: "George S. Coker, II" <gscoker@alpha.ncsc.mil>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
