They'd be easy to add, but "fast" floats are pretty much in limbo right now. They're not exposed to stable, and there's no plan to do so. So there's not really a reason for the compiler team to take the cost of having intrinsics for them.
Here's one of the many other IRLO threads discussing what to do with them: Suggestion: FFastMath intrinsics in stable - #60 by scottmcm