CoreText SDK 10.5 compatibility

Change-Id: Ic876ec473b1c03a70c160af4251c68b299b27eca
Reviewed-on: https://gerrit.libreoffice.org/7143
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>