rust/library at 796bc7cae364b39ff7e5139842b51dd9b764060d - rust

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Yuki Okushi 796bc7cae3 Rollup merge of #98383 - m-ou-se:remove-memory-order-restrictions, r=joshtriplett

Remove restrictions on compare-exchange memory ordering.

We currently don't allow the failure memory ordering of compare-exchange operations to be stronger than the success ordering, as was the case in C++11 when its memory model was copied to Rust. However, this restriction was lifted in C++17 as part of [p0418r2](https://wg21.link/p0418r2). It's time  we lift the restriction too.

| Success | Failure | Before | After |
|---------|---------|--------|-------|
| Relaxed | Relaxed | ✔️ | ✔️ |
| Relaxed | Acquire | ❌                | ✔️ |
| Relaxed | SeqCst  | ❌                | ✔️ |
| Acquire | Relaxed | ✔️ | ✔️ |
| Acquire | Acquire | ✔️ | ✔️ |
| Acquire | SeqCst  | ❌                | ✔️ |
| Release | Relaxed | ✔️ | ✔️ |
| Release | Acquire | ❌                | ✔️ |
| Release | SeqCst  | ❌                | ✔️ |
| AcqRel  | Relaxed | ✔️ | ✔️ |
| AcqRel  | Acquire | ✔️ | ✔️ |
| AcqRel  | SeqCst  | ❌                | ✔️ |
| SeqCst  | Relaxed | ✔️ | ✔️ |
| SeqCst  | Acquire | ✔️ | ✔️ |
| SeqCst  | SeqCst  | ✔️ | ✔️ |
| \*      | Release | ❌                | ❌                |
| \*      | AcqRel  | ❌                | ❌                |

Fixes https://github.com/rust-lang/rust/issues/68464