cs: improve error message for define-values

Report the first variable of the `define-values` form, like
traditional Racket does.

pkgs/racket-test-core/tests/racket/module.rktl

@@ -3158,6 +3158,18 @@ case of module-leve bindings; it doesn't cover local bindings.
                  exn:fail:contract:variable?
                  #rx"struct:spider")))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Make sure error message is right for wrong number of
+;; values
+
+(module returns-obviously-wrong-number-of-values-to-definition racket/base
+  (define-values (x y z) (values 1 2 3 4)))
+
+(err/rt-test/once (dynamic-require ''returns-obviously-wrong-number-of-values-to-definition #f)
+                  exn:fail:contract:arity?
+                  #rx"define-values: result arity mismatch")
+
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/cs/linklet.sls

@@ -1107,7 +1107,7 @@
          (call-with-values proc
            (lambda vals
              (unless (= (length syms) (length vals))
-               (raise-binding-result-arity-error syms vals))
+               (raise-definition-result-arity-error syms vals))
              (let loop ([vars vars] [vals vals] [modes modes])
                (unless (null? vars)
                  (do-variable-set! (car vars) (car vals) (car modes) #t)

racket/src/cs/rumble.sls

@@ -201,6 +201,7 @@
           raise-result-arity-error
           raise-type-error
           raise-binding-result-arity-error ; not exported to Racket
+          raise-definition-result-arity-error ; not exported to Racket
 
           (rename [make-unquoted-printing-string unquoted-printing-string])
           unquoted-printing-string?

racket/src/cs/rumble/error.ss

@@ -431,6 +431,16 @@
          "\n  at: local-binding form"
          args))
 
+(define (raise-definition-result-arity-error expected-args args)
+  (apply raise-result-arity-error 'define-values
+         (length expected-args)
+         (if (null? expected-args)
+             ""
+             (string-append "\n  at: definition of "
+                            (symbol->string (car expected-args))
+                            " ..."))
+         args))
+
 (define raise-unsupported-error
   (case-lambda
    [(id msg)