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

[Artem Belevich via cfe-commits]

https://github.com/Artem-B commented:

Mostly drive-by comments. Don't have strong opinion on either the attributes themselves nor how the values get parsed.

One thing that's missing is the documentation for the attributes. Their format and meaning are far from obvious and should be documented along with other clang-specific attributes.

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