[llvm] [Dexter] Adapt to upcoming lldb stepping behavior (PR #108127)

[Jason Molenda via llvm-commits]

jasonmolenda wrote:

I've never looked at/touched the debuginfo tests / dexter before, I'm not sure who is best to ask to review this change.  I'm open to feedback, I know the comment is a bit long but I wanted to be clear what this was doing.  I wanted to have Dexter work with old or new lldb's equally but people will slowly forget the old lldb behavior.

https://github.com/llvm/llvm-project/pull/108127