[llvm] [RISCV] Support XSfmm LLVM IR and CodeGen (PR #143069)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Is there an ABI specification for this somewhere?  For SME, we did a lot of work to ensure that operations involving the matrix tile work cleanly.  Which... I guess you don't necessarily need to do all of that, but you probably want a spec that says something about it.

https://github.com/llvm/llvm-project/pull/143069