[llvm] [Orc] Add NotifyCreated callback for LLJITBuilder (PR #84175)

[Lang Hames via llvm-commits]

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

I think it makes sense for `NotifyCreated` to return `Error` rather than `void` so that the callback itself can fail. Otherwise this looks great -- thanks @weliveindetail!

https://github.com/llvm/llvm-project/pull/84175