[llvm] [polly] [delinearize] remove all uses of GEP instructions (PR #156215)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

It's good to see the flow from beginning to end, but I think we want to comment on the patches individually and merge them separately, so I think each change needs its own merge request. 

https://github.com/llvm/llvm-project/pull/156215