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

[Matthew Maurer via cfe-commits]

maurer wrote:

Flag guarding this feature seems like it would also be good for any existing C users - for example, if trying to build a kernel module intended to load against a kernel image built with an older `clang`, you need to select the same type ID projection that the kernel did.

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