[llvm] TableGen: Emit perfect hash function for runtime libcalls (PR #150192)

[Eli Friedman via llvm-commits]

https://github.com/efriedma-quic approved this pull request.

This is not really a "perfect hash" in the traditional sense; this is just constructing a conventional hashtable at compile-time with optimized table and bucket sizes.  Maybe tweak the commit message a bit to reflect that.

Otherwise LGTM

https://github.com/llvm/llvm-project/pull/150192