dired-mark-files-regexp checks the NAME of a symbolic link.
Its useful to introduce one function which look for a match
in the TARGET of the symbolic links.
Such function could be bound to '%@'.

In GNU Emacs 25.1.50.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.29)
Repository revision: 25c5651951ef39f650927652dac8b4bbfccb60fa