[clang] [llvm] [CodeGen][KCFI] Switch type hash from xxHash64 to FNV-1a (PR #167254)

[Sami Tolvanen via llvm-commits]

samitolvanen wrote:

What is your plan for addressing compatibility with rustc? If Clang switches to a different hash, the user will also need a version of rustc that uses the same hash, or cross-language indirect calls will break.

https://github.com/llvm/llvm-project/pull/167254