Best place to call xdebug helper functions?

They recommend putting it into the wp-config.php file.

You can read more about it from the codex Editing wp-config

It is quite a long document but the error info is found at 2.15 Configure Error Logging

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