[clang] [Clang][attr] Add cfi_salt attribute (PR #141846)

[Bill Wendling via cfe-commits]

bwendling wrote:

@efriedma-quic Okay, I'm not entirely sure I understand @erichkeane's concerns, but that's fine. Are you suggesting adding the salt information to the `FunctionType` instead?

https://github.com/llvm/llvm-project/pull/141846