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

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

Note: please don't forced push to update PR unless it's really necessary: https://llvm.org/docs/GitHub.html#updating-pull-requests

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