The configure detection is bumped to X265_BUILD >= 68,
since API version 68 corresponds with the x265 1.8
release tarball. The warnings inside x265 about
12-bit being experimental were removed prior to API
version 72 a short time later. At this time of
writing, X265_BUILD is at version 80.
12-bit support in the HEVC standard was approved in
October 2014 as part of HEVC Version 2 and published
in January 2015: