[llvm] [llvm][ABI] Add ABIInfo infrastructure and X86_64/BPF classifiers (PR #190684)

[via llvm-commits]

vortex73 wrote:

I'm already working on upstreaming it [here](https://github.com/llvm/llvm-project/pull/190730) with the X86 and BPF bits to follow :)

https://github.com/llvm/llvm-project/pull/190684