[llvm] [RISCV] Undo fneg (fmul x, y) -> fmul x, (fneg y) transform (PR #157388)

[Craig Topper via llvm-commits]

topperc wrote:

> I'm pretty sure this requires the nsz fast math flag.

I take that back. That might be for the full (fneg (fma)) case.

https://github.com/llvm/llvm-project/pull/157388