unbreak cify build

Handle `(case-lambda)`.

racket/src/cify/arg.rkt

@@ -27,6 +27,10 @@
      (if (list? ids)
          (values min-a min-a)
          (values min-a -1))]
+    [`(case-lambda)
+     (if precise-cases?
+         (values -1 "\"\"")
+         (values 0 0))]
     [`(case-lambda [,unsorted-idss . ,_] ...)
      (cond
        [precise-cases?

racket/src/cify/generate.rkt

@@ -121,7 +121,9 @@
          (out-open "~aif (c_argc ~a ~a) {" (if (zero? i) "" "else ") (if (list? ids) "==" ">=") (args-length ids))
          (generate-lambda-case lam leaf? `(lambda ,ids . ,body) free-var-refs closure-offset)
          (out-close "}"))
-       (out "else return c_wrong_arity(~s, c_argc, c_argv);" (format "~a" id))])
+       (out "~areturn c_wrong_arity(~s, c_argc, c_argv);"
+            (if (null? idss) "" "else ")
+            (format "~a" id))])
     (when bracket? (out-close "}")))
 
   ;; Returns a boolean indicating whether the functon can be a leaf