[llvm] [X86] Don't rely on global contraction flag (PR #167252)

[Phoebe Wang via llvm-commits]

phoebewang wrote:

> > Should we warn `fp-contract` is not used on X86?
> 
> It's not used by the X86 backend, but target independent code still uses it, so IR without `contract` on IR but with `--fp-contract=fast` on CLI may still emit FMA in the end

I think that would be a behavioral change for those who used `--fp-contract=fast` before. So ideal, they should be reminded not to use it any more.

https://github.com/llvm/llvm-project/pull/167252