Auto merge of #152747 - nnethercote:bring-back-enum-DepKind, r=Zalathar

Bring back `enum DepKind`.

*[View all comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust/pull/152747)*

It was removed in rust-lang/rust#115920 to enable it being moved to `rustc_query_system`, a move that has recently been reversed. It's much simpler as an enum.

r? @Zalathar