SVN install of CiviCRM 4 - Smarty error: unable to write to $compile_dir '/tmp/templates_c'

Here is the command line output of GenCode.php:

<pre>
$ php GenCode.php
Parsing input file schema/Schema.xml
Extracting database information
Extracting table information
Generating tests truncate file
Generating sql file
PHP Fatal error: Smarty error: unable to write to $compile_dir '/tmp/templates_c'. Be sure $compile_dir is writable by the web server user. in /var/aegir/platforms/civicrm-4-drupal-7.8-build-1/sites/all/modules/civicrm/packages/Smarty/Smarty.class.php on line 1093
</pre>

In my civicrm.settings.php, the following directory is defined:

define( 'CIVICRM_TEMPLATE_COMPILEDIR', DRUPAL_ROOT . '/sites/dev.civicrm.d7.local/files/civicrm/templates_c' );

With drupal_root defined as:

define('DRUPAL_ROOT', '/var/aegir/platforms/civicrm-4-drupal-7.8-build-1');