CxxUtils: add helpers to enable/disable core files

Add helper functions to Athena::SealDebug to enable/disable core files (equivalent to what can be achived by ulimit -Sc in bash). This can be useful in code to diagnose rare crashes but without enabling core files for the entire application to avoid filling up local disks in case of unrelated crashes.

Let's hope this also compiles on macOS. I really didn't bother to make this Windows-compatible 😉