[llvm] [AMDGPU] Fix legalization of frem(-0.0, y) (PR #70448)

[Jay Foad via llvm-commits]

jayfoad wrote:

Actually there is still interest in this, either for its own sake (to follow the LLVM definition in LangRef) or because the SPIR-V definition may change to match the LLVM definition.

https://github.com/llvm/llvm-project/pull/70448