Function unwrap_fn_abi

fn unwrap_fn_abi<'tcx>(
    abi: Result<&'tcx FnAbi<'tcx, Ty<'tcx>>, &'tcx FnAbiError<'tcx>>,
    tcx: TyCtxt<'tcx>,
    item_def_id: LocalDefId,
) -> &'tcx FnAbi<'tcx, Ty<'tcx>>