[llvm] [Exegesis][RISCV] Add initial RVV support (PR #128767)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

> LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-multistage` running on `ppc64le-clang-multistage-test` while building `llvm` at step 4 "build stage 1".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/76/builds/7363
> 
> Here is the relevant piece of the build log for the reference

This is fixed by 8c5cd773228a6c3fd1c274d32e20508ba5acee97

https://github.com/llvm/llvm-project/pull/128767