suppress some warnings for Ocaml 3.12
suppress some warnings for Ocaml 3.12

jpdeplaix/why3,jpdeplaix/why3,douglas-larocca/why3,douglas-larocca/why3,douglas-larocca/why3,ssaavedra/why3,ssaavedra/why3,jpdeplaix/why3,ssaavedra/why3