[llvm] [PowerPC] Remove `UnsafeFPMath` uses (PR #154901)

[via llvm-commits]

paperchalice wrote:

> @paperchalice We've run into a 'Cannot Select' regression caused by this PR. Here is the reduced test case:
> 
> ```
> ; ModuleID = 'reduced.bc'
> target datalayout = "e-m:e-Fn32-i64:64-i128:128-n32:64-S128-v256:256:256-v512:512:512"
> target triple = "ppc64le-redhat-linux-gnu"
> 
> define fastcc <2 x double> @_ZN3hwy8N_EMU1289TestRoundclIdNS0_4SimdIdLm2ELi0EEEEEvT_T0_(<2 x double> %wide.load13) {
> iter.check:
>   %0 = tail call <2 x double> @llvm.nearbyint.v2f64(<2 x double> %wide.load13)
>   ret <2 x double> %0
> }
> 
> ; Function Attrs: nocallback nofree nosync nounwind speculatable willreturn memory(none)
> declare <2 x double> @llvm.nearbyint.v2f64(<2 x double>) #0
> 
> attributes #0 = { nocallback nofree nosync nounwind speculatable willreturn memory(none) }
> ```

#166307

https://github.com/llvm/llvm-project/pull/154901