fix marshaling of a compiled top-level begin-for-syntax

Closes #1174

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

@@ -1952,6 +1952,15 @@
         procedure?
         (eval (datum->syntax #'here '(lambda () (sort '(1))) (list 'a #f #f #f #f)))))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Check marshaling of a top-level `begin-for-syntax`:
+
+(parameterize ([current-namespace (make-base-namespace)])
+  (eval '(require (for-syntax racket/base)))
+  (write (compile '(begin-for-syntax
+                    (require racket/match)))
+         (open-output-bytes)))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 (report-errs)

racket/src/racket/src/marshal.c

@@ -463,7 +463,7 @@ static Scheme_Object *read_begin_for_syntax(Scheme_Object *obj)
 
 static Scheme_Object *write_begin_for_syntax(Scheme_Object *obj)
 {
-  return write_define_values(obj);
+  return scheme_clone_vector(obj, 0, 0);
 }
 
 static Scheme_Object *read_set_bang(Scheme_Object *obj)