[clang] [clang] Mark some language options as benign. (PR #131569)

[Michael Spencer via cfe-commits]

https://github.com/Bigcheese approved this pull request.

lgtm with Chuanqi's release notes request.

Separately, I'd also like to see the rtti and exceptions stuff be marked compatible, although with some testing first of what happens when people do create AST differences with the macros. It's fine to error (as long as the diagnostic isn't terrible), I just want to know that we won't just crash.

https://github.com/llvm/llvm-project/pull/131569