[llvm] LangRef: state explicitly that floats generally behave according to IEEE-754 (PR #102140)

[Ralf Jung via llvm-commits]

RalfJung wrote:

@jcranmer-intel @andykaylor I think I resolved/answered all of your comments, please let me know if there's anything else to do. :)

https://github.com/llvm/llvm-project/pull/102140