Overview
--------

This fixes a recent regression in which `xml/GenCode.php` fails to execute in certain configurations.

Initial report: https://github.com/civicrm/civicrm-buildkit/issues/503

Before
------

* If the folder `l10n` exists in its traditional location, and if you run `./bin/setup.sh -g`, then it
  correctly executes.
* If the folder `l10n` does not exist in its traditional locacation, and if you run `./bin/setup.sh -g`,
  then it fails with an error like this:
  ```
  + php -d mysql.default_host=127.0.0.1:3306 -d mysql.default_user=dmasterciv_abcde -d mysql.default_password=abcd1234 GenCode.php schema/Schema.xml '' Drupal

  civicrm_domain.version := 5.23.alpha1

  Parsing schema description schema/Schema.xml
  Extracting database information
  Extracting table information
  PHP Fatal error:  Uncaught RuntimeException: Invalid configuration: the [cms.root] path must be an absolute URL in /home/me/.../Civi/Core/Paths.php:1...