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 doesn't have a working symbolicator yet, but it does build and
it can obtain a basic backtrace.
It also doesn't include a working `swift-backtrace` program yet.
rdar://101623384
Changed the way swift-backtrace works for JSON, so that it captures
into a CrashLog, then writes to JSON from the CrashLog. Separating out
the two sets of logic so that writing the CrashLog to JSON becomes
simpler and more modular.
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
Alastair Houghton
Carl Peto