[llvm] [RISCV] Add ISel patterns for Xqciac QC.MULIADD instruction (PR #147661)

[Sam Elliott via llvm-commits]

https://github.com/lenary commented:

Sorry, this is a pretty low-quality review.

The pattern is added, and works, so I'm happy, but I don't have an opinion on whether this is the right way to do this.

https://github.com/llvm/llvm-project/pull/147661