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

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > What's the story for folks that're using `Options.UnsafeFPMath`? Do they need to migrate to using the attribute instead?
> 

Yes

> 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. 

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