[llvm] [LangRef] adjust IR atomics specification following C++20 model tweaks. (PR #77263)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

The content of the patch seems fine.

Can we come up with links that are more likely to be stable?  In particular, eel.is is just someone's personal server.

https://github.com/llvm/llvm-project/pull/77263