Extend invalid_atomic_ordering for compare_exchange{,_weak} and fetch_update

[thomcc]

changelog: The invalid_atomic_ordering lint can now detect misuse of compare_exchange, compare_exchange_weak, and fetch_update.

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I was surprised not to find an issue or existing support here, since these are the functions which are always hardest to get the ordering right on for me (as the allowed orderings for fail depend on the success parameter).

I believe this lint now covers all atomic methods which care about their ordering now, but I could be wrong.

Hopefully I didn't forget to do anything for the PR!

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @phansch (or someone else) soon.

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[phansch]

LGTM implementation wise! However, I haven't used atomics at all, so would prefer a second review from @flip1995

[flip1995]

LGTM. But I think the examples in the documentation could benefit from some explanation.

[flip1995]

Thanks! everything LGTM now. Waiting for rustup.

[matthiaskrgr]

@bors r=flip1995

[bors]

📌 Commit 09f7a37 has been approved by flip1995

[bors]

⌛ Testing commit 09f7a37 with merge 44d6439...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: flip1995
Pushing 44d6439 to master...