Reduce number of directly visible entries in compiler settings page

The compiler settings can list several dozen compilers, including symlinks.

While having the symlinks is important for certain cross-compile scenarios, they clutter the normal setup. Something should be done here. Ideas:

1. Mark symlinks (italic, ...)
2. Have a checkbox "all" vs "no symlinks"
3. have symlinked items in a tree sub-level "below" the "real" entries.