[llvm] [RISCV] Sink NOT to be fold into ANDN/ORN/XNOR/VANDN (PR #131632)

[Sam Elliott via llvm-commits]

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

The CodeGen changes here look good to me. I'm less familiar with how exactly the implementation should be written, but the implementation looks clear to me. Please wait another 24 hours in case there are other reviewers with stronger opinions than mine

https://github.com/llvm/llvm-project/pull/131632