[clang] [RISCV][Clang] Added builtin support for experimental Zimop extension (PR #79971)

[Wang Pengcheng via cfe-commits]

https://github.com/wangpc-pp commented:

The code is OK I think.
One question: how will these builtins be used? Are their semantics bound to specific extensions that extend MOPs?

https://github.com/llvm/llvm-project/pull/79971