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

[Fangrui Song via llvm-commits]

MaskRay wrote:

> How does FNV-1a performance compare to xxhash64?
> 
> > [#121070 (comment)](https://github.com/llvm/llvm-project/pull/121070#issuecomment-2583328678)
> 
> @MaskRay Do you think we could take this opportunity to add xxh3_64? Or is FNV-1a good enough?

I hope that KCFI drops xxHash64 (version 2). It's the only in-tree use of version 2 and otherwise we could remove xxHash64.

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