converts a pointer to the code-field (CFA) to point
then to the corresponding link-field (LFA) - in some configurations
this can be a very slow operation since the system might need to walk
through all header-words in the system, looking for a >NAME that
has the cfa and *then* returning the "N>LINK" result here - which might
be none at all if the word is a :NONAME. Use always >NAME and
treat this word as non-portable just like any assumption about the
contents of the >LINK-field.
Only in fig-mode and for traditional fig-mode programs, this word may
possibly have enough extra assertions to be somewhat reliable.
(and fig-mode did not know about SYNONYMs - see note at LINK>).