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

[Kevin P. Neal via llvm-commits]

kpneal wrote:

Perhaps something like "If a -0 is given, the sign of the result is unspecified unless otherwise documented."  ?

Then we'd need to document those places where the sign of the zero is "specified". The downside of this I guess is that the nsz documentation would be scattered about. Or maybe that's an upside?

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