[clang] [llvm] [RISCV][MC] Add MC support of Zibi experimental extension (PR #127463)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

> > > This adds the support of Zibi v0.1 experimental extension.
> > > References:
> > > 
> > > * https://lf-riscv.atlassian.net/wiki/spaces/USXX/pages/599261201/Branch+with+Immediate+Zibi+Ratification+Plan
> > 
> > 
> > I cannot for the life of me find an actual specification linked from that page, nor from searching. Where is the GitHub repo in the riscv organisation with it?
> 
> There’s no public GitHub repo for Zibi yet. It’s currently going through the ratification process, the repo hasn’t been created at this stage. Please refer to the attachment in [RVS-3828](https://lf-riscv.atlassian.net/browse/RVS-3828) for more details.

I’m not sure we should be merging support for extensions that are so early in the development process that they don’t even have a GitHub repository in the riscv organisation with a specification.

https://github.com/llvm/llvm-project/pull/127463