[llvm] [IR] Remove the possibility of ConstantExpr having fast-math flags. (PR #94507)

[Nikita Popov via llvm-commits]

nikic wrote:

It would be good to also make the class inherit from Instruction instead of Operator (in this context, "Operator" means "Instruction or ConstantExpr").

https://github.com/llvm/llvm-project/pull/94507