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

[Jay Foad via llvm-commits]

jayfoad wrote:

The motivation for this has gone away. I wanted it for Vulkan/SPIR-V but it turns out that SPIR-V does not specify the sign of a zero result from OpFRem.

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