Got it working by reinstalling XAMPP like so:
1. Uninstall XAMPP using the unistaller found at /Applications/XAMPP/uninstall.app
,
2. Delete the leftovers from /Applications/XAMPP/
,
(backup /Applications/XAMPP/xamppfiles/htdocs
and databases if necessary) then
3. Install XAMPP using installer again.
Afterwards, the missing mysql.sock and proper links to it are back to normal and $ mysql
works.