Traits an enum has without an `impl`

Decided

D-0054, settled by the language’s author: part of spec §18. Older text cites it as 18.54.

Eq, Hash and Ord, as the integers they are. Equality and order compare values — declaration order when values are implicit — and a hash is the value’s. So an enum is a HashMap key and satisfies T: Ord with nothing written (§7.4)