[llvm] LangRef: Clarify llvm.minnum and llvm.maxnum about sNaN (PR #112852)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Say you write `fmax(x+0, y)`, and x is an snan.  The result is unpredictable unless you use constrained intrinsic.  If we optimize out the "+0", it produces qnan; if we don't, it returns 1.0.

https://github.com/llvm/llvm-project/pull/112852