[llvm] [CodeGen] Provide `MachineFunction::hasUnsafeFPMath` (PR #127488)

[Kevin P. Neal via llvm-commits]

kpneal wrote:

> > Some backends use this option to control the behavior of legalizer. Ideally backend should consider both `Options.UnsafeFPMath` and "unsafe-fp-math" function attribute.
> 
> No, Options.UnsafeFPMath should be purged. unsafe-fp-math should also be removed, but that's more difficult.
> 
> Users should never use --enable-unsafe-fp-math. It's only for lit tests. The cl::opt is still used in many tests, but is implemented by setting the attribute on functions that do not have have the attribute already.

This seems like the sort of thing that should be made obvious in user-facing documentation.

https://github.com/llvm/llvm-project/pull/127488