InspIRCd: add optional deps, skip_clean

  - Add options for installing all non-standard modules
  - Prefer system-provided modules (e.g. OpenSSL over GnuTLS)
  - Don't delete the 'data' and 'logs' directories when cleaning

Closes #17996.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
lftp: add mirror

Closes #18219.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>