Caught by clang in #778,
This line causes a warning - num_symbols is unsigned, it should be at least signed (and, according to some other bfd_* usage on the web, long).
As a result, we probably can't detect when we fail to read symbols from object files.
Fix types of size, num_symbols in fancy_backtrace. Close #779
What it doesn't fix, though is the fact that libiberty isn't shipped
by homebrew's binutils anymore, cf:
Apparently we should be shipping our own sources, but seeing our
delicate build process, it seems unrealistic for now.