- root for -C or -D, the caller must either be root or the Exim user
- defined in the binary (when deliver_drop_ privilege is false).
-
-If ALT_CONFIG_ROOT_ONLY is defined, we don't know whether we were called by the
-built-in exim user or one defined in the configuration. In either event,
-re-enable log processing, assuming the sysadmin knows what they are doing. */