Function compute_sig_of_foreign_fn_decl

fn compute_sig_of_foreign_fn_decl<'tcx>(
    tcx: TyCtxt<'tcx>,
    def_id: LocalDefId,
    decl: &'tcx FnDecl<'tcx>,
    abi: ExternAbi,
    safety: Safety,
) -> PolyFnSig<'tcx>