persistent_add FLTK_SUBOPTS
case $THIS_SUB_DEPENDS in
            THREAD) list_add FLTK_SUBOPTS '--enable-threads'  ;;
            OPENGL) echo "OPENGL support requested, forcing OPENGL dependency." &&
                 depends OPENGL --enable-gl
                 ;;
*) message "${PROBLEM_COLOR}bogus sub_depends: $SPELL $THIS_SUB_DEPENDS${DEFAULT_COLOR}" ;
   return 1;;
esac
