allow build with icu 4.2

Change-Id: I4bbcff7963520426d4c04e15d2239431aff65b56
Reviewed-on: https://gerrit.libreoffice.org/10042
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>