For some reason we don't see the dyld frames in CI. That's fine, don't
check for them.
Also turn NotImportedByDefault off for Windows as it needs a better
shell than the support provided there.
Once the API has gone through Swift Evolution, we will want to implicitly
import the _Backtracing module. Add code to do that, but set it to off
by default for now.
rdar://105394140