Fix old-style function definitions and enable warning. (#1651)

Function definitions with no parameters should always use the void keyword to allow the compiler to catch invalid calls of those functions at compile time.

Enable -Wold-style-definition to catch this early in the future.

Fixes #1649.

JerryScript-DCO-1.0-Signed-off-by: Tilmann Scheller t.scheller@samsung.com

targets/default/jerry-port-default-fatal.c

@@ -36,7 +36,7 @@ void jerry_port_default_set_abort_on_fail (bool flag) /**< new value of 'abort o
  * @return true - if 'abort on fail' flag is set,
  *         false - otherwise.
  */
-bool jerry_port_default_is_abort_on_fail ()
+bool jerry_port_default_is_abort_on_fail (void)
 {
   return abort_on_fail;
 } /* jerry_port_default_is_abort_on_fail */