error log cluttered with undefined DB_USER wp-admin/setup-config.php

You can place a .htaccess file in the folder wp-admin with the following content:

<Files "setup-config.php">
Order Deny,Allow
Deny from all
</Files>

Optionally you can add the line Allow from {your ip address} after Deny from all, so you can access the file.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)