[llvm] [llvm][mc][riscv] MC support of T-Head vector extension (xtheadvector) (PR #84447)

[Chris Lattner via llvm-commits]

lattner wrote:

Super awesome @kata-ark thank you for doing this.  I'm sorry for the back and forth on this, but it is very important to LLVM to make sure to protect the rights of people who are innovating and creating things, which means we have to be careful about derivative works.  I am very happy you're pushing forward here and are trying to make LLVM better, I'm sorry it cost you a bit of time, but this sort of thing helps make LLVM stronger in the long run.  Thank you!

https://github.com/llvm/llvm-project/pull/84447