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

[Sushant Gokhale via llvm-commits]

sushgokh 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 show 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.

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