[llvm] [SelectionDAG] Salvage debug info for non-constant ADDs (PR #68981)

[David Stenberg via llvm-commits]

dstenb wrote:

This broke expensive-checks buildbots, e.g. https://lab.llvm.org/buildbot/#/builders/16/builds/56317, so I'll revert and investigate.

https://github.com/llvm/llvm-project/pull/68981