[llvm] [DebugNames] Implement Entry::GetParentEntry query (PR #78760)

[Greg Clayton via llvm-commits]

https://github.com/clayborg commented:

Looks good. The only question that comes to mind is if we want APIS with both expected and optional in the return value. Double unwrapping required for each, and for the errors that are returned in this patch, they are just consumed and ignored.

https://github.com/llvm/llvm-project/pull/78760