[clang] [llvm] [X86] Enhance kCFI type IDs with a 3-bit arity indicator. (PR #117121)

[Scott Constable via cfe-commits]

scottconstable wrote:

> If you are changing the hash scheme, please migrate from xxHash64 to xxh3. We want to remove the legacy xxHash64 from LLVM.

It seems from the discussion above that this change would require a new flag. Suppose, for instance, that a user builds a kernel with a version of Clang that uses xxh3, and a version of rustc that still uses xxHash64. Then the hashes could be incompatible and the kernel will crash.

This PR is specific to X86-64 targets. Your suggestion seems like a general enhancement that should apply to all targets; I think it should be a separate PR.

https://github.com/llvm/llvm-project/pull/117121