[llvm] [clang] [RISCV] Remove experimental from Vector Crypto extensions (PR #74213)

[Eric Biggers via llvm-commits]

ebiggers wrote:

> To be safe, I think we should have an experimental tag to guard the intrinsics, while the extension is ratified and do indeed don't need the experimental.

This is already part of the pull request.

I've updated the commit message and pull request description to make it clear that it's still leaving the C intrinsics as experimental.

> What you propose here seems OK to me, but please add something to RISCVUsage indicating that in some cases an extension may be non-experimental but the intrinsics still experimental and -menable-experimental-extensions must be passed to Clang to use them.

I added a new section "Experimental C Intrinsics" to RISCVUsage.rst.

Also in RISCVUsage.rst, I changed the status of the extensions from "Supported" (the previous proposal) to "Assembly Support".  This is consistent with the fact that the file says that "Supported" means the C intrinsics are supported.

> I also think a Clang release note might make sense, such as "It is now possible for intrinsics to be experimental while the extension itself is non-experimental. This is currently the case for the vector crypto extensions (Zvk*, Zvbb, Zvbc) where -menable-experimental-extension must still be passed to Clang in order to enable use of the C intrinsics."

Done, but I combined the information with the note already being added about the vector crypto extensions, since that seems to be more logical.  Let me know what you think; thanks!

https://github.com/llvm/llvm-project/pull/74213