[clang] [clang] Function type attribute to prevent CFI instrumentation (PR #135836)

[via cfe-commits]

PiJoules wrote:

> For the new test files, is it possible to precommit them? I think it will be easier to review the delta.

I'll precommit once folks think this is ok at a high level. Wouldn't want to potentially rewrite tests if the implementation happens to change a lot.

https://github.com/llvm/llvm-project/pull/135836