We need a minimum target of 15.7 or below because of CI, so add a new
`BacktracingDT 6.2` define. This is a bit of a hack for now to
unblock CI upgrades; we can go and clean things up and perhaps
generalise this mechanism later.
rdar://172129091
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
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
Allan Shortlidge
Alastair Houghton