[llvm] [SDAG] Use useDebugInstrRef instead of shouldUseDebugInstrRef (PR #160686)

[Jeremy Morse via llvm-commits]

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

LGTM, I think this matches my expectations for those functions. The primary reason for this facility existing is that SelectionDAG changed the optimisation-level flags according to things like function attributes. This made it important to a) pick which "mode" of debugging-information was to be in at one point in time, and b) to store that independently of any other information.

(Perhaps things have changed since then; but that's the motivation behind the code).

https://github.com/llvm/llvm-project/pull/160686