These were apparently accidentally disabled on all non-WNT platforms.
Set the OPT variable from the outside on the platform that needs it.
(regression from ab41efc81ec26fcbd4cdeb9c36fbe8cc274523f)

Change-Id: Ifbf7ec8e0f863cb6368758571496c8b615e3e814
(cherry picked from commit 38232ea1)
Reviewed-on: https://gerrit.libreoffice.org/3472Reviewed-by: Fridrich Strba <fridrich@documentfoundation.org>
Tested-by: Fridrich Strba <fridrich@documentfoundation.org>