[clang] [llvm] [RISC-V] Add CSR read/write builtins (PR #85091)

[Alex Bradbury via llvm-commits]

asb wrote:

> In my view, the builtin solution is superior from a usability perspective.

I agree, I think Sam's previous work on this stopped due to changing priorities not because there was any real pushback.

https://github.com/llvm/llvm-project/pull/85091