rent`.

`compare_exchange` takes two [`Ordering`] arguments to describe the memory
ordering of this operation. `success` describes the required ordering for the
read-modify-write operation that takes place if the comparison with `current` succeeds.
`failure` describes the required ordering for the load operation that takes place when
the comparison fails. Using [`Acquire`] as success ordering makes the store part
of this operation [`Relaxed`], and using [`Release`] makes the successful load
[`Relaxed`]. The failure ordering can only be [`SeqCst`], [`Acquire`] or [`Relaxed`].

# Panics

Panics if `failure` is [`Release`], [`AcqRel`].

# Examples

```
use portable_atomic::{