Pass legacy const runtime flag to preparser appropriately

test/message/const-decl-no-init-sloppy.out

Index: test/message/const-decl-no-init-sloppy.out
diff --git a/test/message/regress/regress-4829-1.out b/test/message/const-decl-no-init-sloppy.out
similarity index 52%
copy from test/message/regress/regress-4829-1.out
copy to test/message/const-decl-no-init-sloppy.out
index 61b72a5bd7aadea8477e26cc19991588ca4bc600..302497771a3a57ae6d3b3948d82cccaa4880de24 100644
--- a/test/message/regress/regress-4829-1.out
+++ b/test/message/const-decl-no-init-sloppy.out
@@ -1,8 +1,7 @@
 # Copyright 2016 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
-
-*%(basename)s:7: SyntaxError: Invalid or unexpected token
-tag(tag`\xyy`);
-       ^^^
-SyntaxError: Invalid or unexpected token
+*%(basename)s:8: SyntaxError: Missing initializer in const declaration
+  const a;
+        ^
+SyntaxError: Missing initializer in const declaration