Pass legacy const runtime flag to preparser appropriately

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 12666fe8ef4fe5ecbe715897dc6de69ff7644816..058f23114072ddf28b9d7562b9708fa9e9be4f78 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -4675,6 +4675,7 @@ PreParser::PreParseResult Parser::ParseLazyFunctionBodyWithPreParser(
     reusable_preparser_->set_allow_lazy(true);
 #define SET_ALLOW(name) reusable_preparser_->set_allow_##name(allow_##name());
     SET_ALLOW(natives);
+    SET_ALLOW(legacy_const);
     SET_ALLOW(harmony_sloppy);
     SET_ALLOW(harmony_sloppy_let);
     SET_ALLOW(harmony_do_expressions);