On-crash backtracing is basically there for 64-bit Windows. It
won't work on 32-bit because of a Swift compiler issue, and there
is a little more work to do yet, but it is now working!
rdar://101623384
This is slightly complicated by us currently not supporting this code
on iOS/tvOS/watchOS/visionOS. We should fix that, at which point we
can use the `SwiftStdlib`/`StdlibDeploymentTarget` macros instead.
rdar://164850733
Move the backtracing code into a new Runtime module. This means renaming
the Swift Runtime's CMake target because otherwise there will be a name
clash.
rdar://124913332
