[llvm] [DAG] Prefer 0.0 over -0.0 as neutral value for FADD w/NoSignedZero (PR #106616)

[Matt Arsenault via llvm-commits]

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

Not sure why this function isn't called getIdentityValue like in other places 

https://github.com/llvm/llvm-project/pull/106616