coinmp: actually link the libraries

Several people named Chris report failures in the solver unit test, and
apparently the CoinMP libraries have loads of unresolved symbols
because they don't have NEEDED entries, i.e. were not linked properly;
let's see if this fixes it.

Change-Id: Id406e14b0805a458d608c23cb7c65d873b5ba2f0
Reviewed-on: https://gerrit.libreoffice.org/8850
Reviewed-by: Chris Laplante <mostthingsweb@gmail.com>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>