[Clang][OpenMP] Enable floating-point operation for `atomic compare` series

D127041 introduced the support for `fmax` and `fmin` such that we can also reprent
`atomic compare` and `atomic compare capture` with `atomicrmw` instruction. This
patch simply lifts the limitation we set before.

Depend on D127041.

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D127042