makes the store part of this operation [`Relaxed`], and
using [`Release`] makes the load part [`Relaxed`].

# Examples

```
use portable_atomic::{AtomicI64, Ordering};

let foo = AtomicI64::new(0b101101);
assert_eq!(foo.fetch_xor(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b011110);
```