This is necessary to avoid having extra threads
while forking. After forking, the second stage
of pre-init is started and so we start the stopped
rtl threads.

The comment for rtl_alloc_preInit_phase_t has
more details.

Change-Id: I1a3f7be74d4b04d0b2fc4a72b02124c2faa3c047
Reviewed-on: https://gerrit.libreoffice.org/47060Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Ashod Nakashian <ashnakash@gmail.com>