[clang] [llvm] [RISCV] Add MC layer support for XSfmm*. (PR #133031)

[Philip Reames via llvm-commits]

preames wrote:

We have discussed whether to accept non-conforming vendor extensions in the past.  Our consensus was clearly documented in RISCVUsage.rst in the statement " In particular, we expect to eventually accept both custom extensions and non-conforming extensions."

This is a non-conforming vendor extension, and that needs to be clearly described, but it is not blocking for whether we accept the change.  



https://github.com/llvm/llvm-project/pull/133031