[llvm] LangRef: Clarify behaviors of nsz in fast math flag (PR #137567)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Maybe I'm missing some context as to why this was needed

I think the problem is alive2's interpretation of nsz maxnum(+0, +0) assumes -0 is a valid output 


https://github.com/llvm/llvm-project/pull/137567