It's useful to capture the platform and platform version with the image map.
Also, display both the platform and architecture information when generating
a crash log.
rdar://124913332
Also removed a spurious `print()` that got left in by accident,
and disabled the `CodableBacktrace.swift` test on Linux since we
need Foundation and we don't have it there.
rdar://124913332
We want to be able to efficiently serialise lists of images, and to do so
it makes most sense to create a separate `ImageMap` type. This also provides
a useful place to put methods to e.g. find an image by address or by build
ID.
rdar://124913332
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
