fdo#63756 build libxml2 with ICU support

Change-Id: I0523e49e640812be435ba4c97b1881ca253eb2ab
(cherry picked from commit 7515b1a90fac9e31733c0fdcc1156adadf0e6f99)
Reviewed-on: https://gerrit.libreoffice.org/10428
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>