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

[James Y Knight via llvm-commits]

jyknight wrote:

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

I don't think there are "official" HTML links; eel.is is a widely-referenced url for this.

However, I swapped the link to https://eel.is/c++draft/atomics.order for the marginally-more-official-perhaps https://wg21.link/atomics.order  which is currently a redirect to the former. I didn't see a redirect to the toplevel of the spec (which I referenced in Atomics.rst), so I just left that "unofficial latest C++ draft". It's right next to a link to isocpp.org for the final C++20 anyhow, so if it goes away there's still a usable link.

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