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

[Jay Foad via llvm-commits]

jayfoad wrote:

It has been pointed out to me that this also changes the sign of the result when the division `x / y` overflows.

Previously: frem(huge, tiny) -> infinity with opposite sign from x
Now: frem(huge, tiny) -> infinity with same sign as x

I'm not sure if this is a good thing or a bad thing.

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