[llvm] [RISCV] Match vcompress during shuffle lowering (PR #117748)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM. I'm not concerned about the lack of masking, I think the benefit of being able to sometimes materialize the mask as a single li + vmv.s.x is enough to outweigh it.

https://github.com/llvm/llvm-project/pull/117748