This updates the vendor'd libbacktrace source to tpick up
gcc-mirror/gcc@047a1c2f which is a soundness fix for when a backtrace is
generated on executables that do not have debug information.
These should probably be submitted upstream. They're inevitably going to
complicate merges, and because they're non-functional changes this just
isn't worth our time.
Remove leading newlines; replace lines containing only whitespace with empty lines; replace multiple trailing newlines with a single newline; remove trailing whitespace in lines
Fix formatting
Remove unused imports
Refactor
Fix msvc build
Fix line lengths
Formatting
Enable backtrace tests
Fix using directive on mac
pwd info
Work-around buildbot PWD bug, and fix libbacktrace configuration
Use alternative to `env -u` which is not supported on bitrig
Disable tests on 32-bit windows gnu
