[clang] [llvm] [RISCV] Add Supm extension to RVA23 profiles (PR #113619)

[Alex Bradbury via cfe-commits]

asb wrote:

> LGTM. (And it's time to mark RV[A|B|M]23 as non-experimental now?)

RVA23 and RVB23 yes. RVM23 isn't ratified yet. I've got a couple of other patches like this to lay the groundwork before flipping the switch.

https://github.com/llvm/llvm-project/pull/113619