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
