Boundary symbols have a special name prefix:

* section$start$segname$sectname
* section$stop$segname$sectname
* segment$start$segname
* segment$stop$segname

and will resolve to either start or end of the respective
section/segment if found.

If not found, we return an error stating we couldn't find the
requested section/segment rather than silently failing and resolving
the address to 0 which seems to be the case with Apple's ld64.