allow build with icu 4.2

Change-Id: I4bbcff7963520426d4c04e15d2239431aff65b56
(cherry picked from commit 414540aecae90774e12390cfcf8f0a37e10684b4)
Reviewed-on: https://gerrit.libreoffice.org/10044
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>