It was also suggested in that thread by P.J. Bourguignon to use
alternate methods, but both required parts of cl (for "every" and
"dolist"), hence I'm submitting this version (and checked that "make
bootstrap" succeeds).

Another version would be something along the lines of:
  (mapc (function (lambda (elt)
                    (if (null (symbolp elt))
                        (error "Malformed arglist: %s" arglist))))
        (if (listp arglist)
            arglist
          '("")))
but it doesn't look more efficient from my (very limited) test.

-- 
Nico.