[clang] [llvm] [Serialization] Use stable hash functions (PR #96136)

[Fangrui Song via cfe-commits]

MaskRay wrote:

This patch fixes most clangSerialization issues if we make `llvm::hash_combine`/`llvm::hash_value` non-deterministic.
https://github.com/MaskRay/llvm-project/tree/hashing-seed

Some check-clang-modules tests still fail (@ChuanqiXu9) along with other failures (e.g. HIP @jhuber6 )

https://github.com/llvm/llvm-project/pull/96136