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

[Matt Arsenault via llvm-commits]

https://github.com/arsenm approved this pull request.

I'm not 100% sure the correctly rounded bit applies to the default sqrt expansion on all targets, but I think we should consider that a bug if it's not.

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