[clang] [llvm] [RISCV] Allow `Zicsr`/`Zifencei` to duplicate with `g` (PR #136842)

[Alex Bradbury via cfe-commits]

asb wrote:

> If you're planning on backporting this, should the release notes be added in a separate commit? I'm wondering if you'll end up with issues trying to cherry-pick it otherwise

I think we'd typically land a change in the most logical way for the main branch and then handle unpicking the backport manually - it just means the tooling needs a little bit of help but it's not complex to manually drop the release note change. I don't feel strongly given what a minor detail it is, but that would be my default.

https://github.com/llvm/llvm-project/pull/136842