[llvm] Revert "Avoid maxnum(sNaN, x) optimizations / folds (#170181)" (PR #184125)

[Ralf Jung via llvm-commits]

RalfJung wrote:

> Now that maxnum(x, sNaN) is specified to non-deterministically produce either qNaN or x,

Nit: it can non-deterministically produce either *NaN* or x. Returning a signaling NaN is also permitted. This follows from the usual [NaN propagation rules](https://llvm.org/docs/LangRef.html#behavior-of-floating-point-nan-values).

https://github.com/llvm/llvm-project/pull/184125