See https://github.com/perl6/roast/blob/03686da5d7f8d8c359e0ce6a538e29dc95e1d218/S04-declarations/multiple.t#L29-L31
Do we *really* want to allow multi subs without multi (when there's a proto)? If so, why? Because you can replace “sub” with a “multi” and it easy to do yet it adds clarity. Is this ticket rejectable?
