Update CMake for 3.12 and newer
Update CMake for 3.12 and newer

 - Get rid of dev warning about [policy CMP0075]
 - See documentation of [CMake policies] for additional info

[policy CMP007]: https://cmake.org/cmake/help/latest/policy/CMP0075.html
[CMake policies]: https://cmake.org/cmake/help/latest/manual/cmake-policies.7.html

sourceryinstitute/opencoarrays,sourceryinstitute/opencoarrays,sourceryinstitute/opencoarrays