Implement var statement pre-scanning. (#3103)

The patch also checks whether pre-scanning is successful when scanning is,
so no need for explicit pre-scanner checks anymore.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/parser/js/js-parser.c

@@ -2544,6 +2544,10 @@ parser_parse_source (const uint8_t *arg_list_p, /**< function argument list */
     compiled_code_p = parser_post_processing (&context);
     parser_list_free (&context.literal_pool);
 
+#ifndef JERRY_NDEBUG
+    JERRY_ASSERT (context.status_flags & PARSER_SCANNING_SUCCESSFUL);
+#endif /* !JERRY_NDEBUG */
+
 #if ENABLED (JERRY_PARSER_DUMP_BYTE_CODE)
     if (context.is_show_opcodes)
     {