[clang] Add clang atomic control options and attribute (PR #114841)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

> The changes should definitely come with a release note in `clang/docs/ReleaseNotes.rst`, but this also seems like it maybe should get wider documentation in the language extensions manual. I mentioned a need for attribute documentation, that could be simple docs which point into the more verbose docs in the language extensions section, perhaps

will do

https://github.com/llvm/llvm-project/pull/114841