swift

72f8aae5 - [Backtracing] Add an indication that we're working on a backtrace.

[Backtracing] Add an indication that we're working on a backtrace. When we crash, emit a message straight away that says we're working on a backtrace. If starting the backtracer fails, report that also. Finally, add a duration to the messages output by the backtracer, so that we can see how long it took. rdar://118055527