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

[Jessica Clarke via cfe-commits]

jrtc27 wrote:

Surely we should instead be defining intrinsics with actual names for the operations we know about? What's the actual use case for needing an arbitrary unnamed one?

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