Get libtiff on the same patch level as Debian. The imported patch file contains:

CVE-2017-9935
CVE-2017-11613
CVE-2017-17095
CVE-2017-18013
CVE-2018-5784
CVE-2018-7456

Re #41748 (master)
Re #41749 (release-18.03 - needs to be cherry-picked)