Auto merge of #95971 - workingjubilee:no-weird-fp-in-const, r=oli-obk

Auto merge of #95971 - workingjubilee:no-weird-fp-in-const, r=oli-obk

No "weird" floats in const fn {from,to}_bits

I suspect this code is subtly incorrect and that we don't even e.g. use x87-style floats in CTFE, so I don't have to guard against that case. A future PR will be hopefully removing them from concern entirely, anyways. But at the moment I wanted to get this rolling because small questions like that one seem best answered by review.

r? `@oli-obk`
cc `@eddyb` `@thomcc`