No impl of Ord for RefCell<T> or Cell<T> when T: Ord

[vadixidav]

Title says it all. I am working on it right now. Do I need to create an RFC or can I just send a PR?

[sfackler]

The implementation for RefCell is not super workable since it would have to either panic or return nonsensical results if the cell is borrowed mutably at the time. An impl for Cell seems like it should be fine though.

[Diggsey]

What's the problem with panicking? That's what borrow() does anyway if there's an outstanding mutable borrow. Given that this is single-threaded, it would be a program error anyway.

[Aatch]

@sfackler there is an impl of PartialEq for RefCell<T: PartialEq>, so PartialOrd/Ord should behave the same way anyway.

[tbu-]

Fixed by #33306.