Use `task_read_for_pid()` rather than having the crashing program pass its
own task port through. This opts us in to additional OS security measures
surrounding the use of this call.
rdar://107362003
The Linux Swift compiler is ICEing when building _Backtracing, while
Windows still needs some tweaks. In order to land this sooner, disable
this code except for macOS.
Some symbolication frameworks have a symbol cache; we probably don't want
to use that for test cases, to avoid running into problems where the cache
holds stale information.
rdar://105409147
This is Swift's external backtracer. It's written in Swift, and it's
responsible for generating nice backtraces when Swift programs crash.
It makes use of the new `_Backtracing` library, which is also (mostly,
aside from some assembly language) implemented in Swift.
rdar://103442000
