Codechange: [MacOS] use backtrace() instead of our custom variant

[TrueBrain]

Motivation / Problem

As mentioned in the comment, we only did it ourselves as we once were compatible with versions before 10.5. But that time has long gone. So let's update the code to a bit more modern approach.

Description

Remove custom backtrace code, and reuse the exact same code as Linux has been using.

Limitations

The output is slightly different, but not in a way that should be any problem to any reader.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker

[glx22]

Assuming you tested it :)