[clang] [llvm] [X86] Extend kCFI with a 3-bit arity indicator (PR #121070)

[Sami Tolvanen via llvm-commits]

samitolvanen wrote:

> A gentle reminder to please review this PR.

Overall this looks fine to me, but I was hoping to get an answer to my question about how the Kconfig detection is actually going to be implemented: https://github.com/llvm/llvm-project/pull/121070#discussion_r1911688455

https://github.com/llvm/llvm-project/pull/121070