[clang] [llvm] [RISCV] Remove experimental from Zacas. (PR #83195)

[Craig Topper via cfe-commits]

topperc wrote:

> LGTM.
> 
> Will it be in LLVM 18? Or we need more time to examine its robustness?

The bar for LLVM 18 is pretty high at this point. I doubt this qualifies.

https://github.com/llvm/llvm-project/pull/83195