[llvm] [SROA] Propagate no-signed-zeros(nsz) fast-math flag on the phi node using function attribute (PR #83381)

[Joshua Cranmer via llvm-commits]

jcranmer-intel wrote:

> > I do think we should have the phase ordering test
> 
> Although I didn't have a PhaseOrdering test, I had initially added a test that showed the transformation after the concerned passes [here](https://github.com/llvm/llvm-project/pull/83381#discussion_r1603994238) and @jcranmer-intel insisted there that this is not required.

The right way to do a phase ordering test is not the way you did it. There's a folder test/Transforms/PhaseOrdering directory where the phase-ordering tests go, and in general, you would probably want to check a test like `opt -O1` to make sure that the passes are actually run in the order expected.

https://github.com/llvm/llvm-project/pull/83381