[llvm] [IR] Store fast-math flags in subclasses of Instruction (PR #191190)

[via llvm-commits]

paperchalice wrote:

> Is there an RFC where the extension of FMF to 16 bits was discussed and what they're going to be used for?

https://discourse.llvm.org/t/rfc-improving-ir-fast-math-semantics/78736 proposed a new flag `bikeshed`.
In https://discourse.llvm.org/t/extending-fast-math-flags/88153, downstream also want to extend fast-math flags.




https://github.com/llvm/llvm-project/pull/191190