[llvm] change contents of ScalarEvolution from private to protected (PR #83052)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

It looks like a lot of the changes here are not really changes from Enzyme, but failures to integrate upstream SCEV changes back into Enzyme's copy. These should be dropped from this patch (and maybe ported to Enzyme's copy independently of this PR?)

https://github.com/llvm/llvm-project/pull/83052