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

[Alexis Engelke via llvm-commits]

aengelke wrote:

Is there an RFC where the extension of FMF to 16 bits was discussed and what they're going to be used for? If so, it would be good to add it to the PR description. If not, it would probably be good to get consensus on the long-term direction first.

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