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

[Matt Arsenault via llvm-commits]

https://github.com/arsenm approved this pull request.

It's not great but was the consensus on the ticket. The phase orderingtest could use a comment and rename though 

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