Add an option so that when the backtracer starts in a crashing process
it will close all unnecessary file descriptors before it tries to start
gathering the backtrace as that may take time.
rdar://144402533
Tweaked the comment in `Runtime/Config.h`.
Fixed a couple of incorrect ARM64 instruction mnemonics. This still needs
testing on ARM64 Windows.
Fixed an out-of-date comment in `swift-backtrace`.
Use a macro in `Backtrace.cpp` to guarantee we don't overrun the buffer,
and in the process simplify the code slightly.
rdar://101623384
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
Carl Peto
Alastair Houghton