Merge topic 'remove-old-compatibility'

3c4afba8cc Remove compatibility with CMake versions older than 2.8.12
0453f70400 CMP0023: Remove support for OLD behavior
033a2dc000 cmLinkItem: Remove now-unused fields from link interfaces
c965856a1d cmGeneratorTarget: Simplify storage of link implementation
888259c894 CMP0022: Remove support for OLD behavior
e31d1c7600 CMP0021: Remove support for OLD behavior
094b42b643 CMP0020: Remove support for OLD behavior
092d6de4be CMP0019: Remove support for OLD behavior
...

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !10195