records: Make 'make-syntactic-constructor' available at load/eval/expand.

* guix/records.scm (make-syntactic-constructor): Wrap in 'eval-when'.

guix/records.scm

@@ -42,6 +42,10 @@
                        (format #f fmt args ...)
                        form))))
 
+(eval-when (expand load eval)
+  ;; This procedure is a syntactic helper used by 'define-record-type*', hence
+  ;; 'eval-when'.
+
   (define* (make-syntactic-constructor type name ctor fields
                                        #:key (thunked '()) (defaults '())
                                        (delayed '()))
@@ -137,7 +141,7 @@ the list of identifiers of delayed fields."
                           (record-error 'name s
                                         "missing field initializers ~a"
                                         (lset-difference eq? 'expected
-                                                       fields))))))))))))
+                                                         fields)))))))))))))
 
 (define-syntax define-record-type*
   (lambda (s)