macroexpand crashes on `->` with `where`

[vtjnash]

;; given the LHS of e.g. `x::Int -> y`, wrap the signature in `tuple` to normalize
(define (tuple-wrap-arrow-sig e)
  (cond ((atom? e)             `(tuple ,e))
        ((eq? (car e) 'where)  `(where ,(tuple-wrap-arrow-arglist (cadr e)) ,@(cddr e)))
        ((eq? (car e) 'tuple)  e)
        ((eq? (car e) 'escape) `(escape ,(tuple-wrap-arrow-sig (cadr e))))
        (else                  `(tuple ,e))))

The tuple-wrap-arrow-arglist function does not exist.

MWE

julia> macro x(); return :((() where T) -> ()); end; @x

(unbound-error tuple-wrap-arrow-arglist)
unexpected error: #0 (tuple-wrap-arrow-sig
 (where (tuple) T))
#1 (resolve-expansion-vars-
 (-> (where (tuple) T) (block (line 1 |REPL[3]|) (tuple))) () #<julia: Main>
 ((line 1 |REPL[3]|)) () #f)
ERROR: syntax: malformed expression

(added by Jeff in 646626e with no test so it was always broken)