[llvm] Don't collect from phi nodes which are not fully constructed yet (PR #140806)

[William Moses via llvm-commits]

wsmoses wrote:

this was resolved in enzyme proper and can be closed [specifically the code was refactored to run all the analyses before generating the initial phis to be filled in, instead of the setup where they were interleaved]

https://github.com/llvm/llvm-project/pull/140806