macos: add support for MacOS 10.14

macos: add support for MacOS 10.14

This commit introduces the new set of changes / files required to
successfully build the OpenAFS source code on OS X 10.14 "Mojave".

Reviewed-on: https://gerrit.openafs.org/13348
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 72b2670a9e2e3937ed4e47485b9e9fa6953b5444)

Change-Id: Ida25278d68d875a630af1d916d2d6add9b6c1f9e
Reviewed-on: https://gerrit.openafs.org/13412
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>