Support strict mode detection in the pre-scanner. (#3450)

Furthermode an error is thrown when 'use strict' is used in a function with non-simple arguments
and function arguments are not moved to lexical environment when unmapped arguments are present.

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

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

@@ -937,6 +937,10 @@ parser_error_to_string (parser_error_t error) /**< error code */
       return "Arguments is not allowed to be used here in strict mode.";
     }
 #if ENABLED (JERRY_ES2015)
+    case PARSER_ERR_USE_STRICT_NOT_ALLOWED:
+    {
+      return "The 'use strict' directive is not allowed for functions with non-simple arguments.";
+    }
     case PARSER_ERR_YIELD_NOT_ALLOWED:
     {
       return "Incorrect use of yield keyword.";