[llvm] [Exegesis][RISCV] Add RISCV support for llvm-exegesis (PR #89047)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

Mostly some nits/cleanup.

There are at least two places where it would be nice to pull bits out into a separate PR. I don't want to block on that, but it would make things a bit easier for reviewers and probably improve the code a bit more.

https://github.com/llvm/llvm-project/pull/89047