[llvm] Optimize fptrunc(x)>=C1 --> x>=C2 (PR #99475)

[via llvm-commits]

kissholic wrote:

> This appears to be incorrect w.r.t. round-to-nearest rounding of fptrunc. [alive2](https://alive2.llvm.org/ce/z/w-496p) The constant needs adjustment.

It seems that the double type the fp constant converted to can express the same value with float type without lossing accuracy. The rmNearestTiesToEven has already been applied, and no difference appeared.🫣

https://github.com/llvm/llvm-project/pull/99475