[llvm] [ConstantFolding] Don't fold constrained fsub/fadd to zero with round.dynamic (PR #184919)

[Matt Arsenault via llvm-commits]

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arsenm wrote:

```suggestion
  %result = call double @llvm.experimental.constrained.fsub.f64(double 0.0, double 0.0, metadata !"round.dynamic", metadata !"fpexcept.strict")
```
Shouldn't need the callsite attributes 

https://github.com/llvm/llvm-project/pull/184919