fix external/coinmp on OSX: bad symlinking

instdir/LibreOfficeDev.app/Contents/MacOS/libCbc.3.dylib -> libCbc.3.8.8.dylib
(which does not exist)

See also: 9f339a89453808b917177a3ee675a76385758902

Change-Id: I398d649c2e918b496c9b92364189da4796682653
Reviewed-on: https://gerrit.libreoffice.org/10614
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>