CMake: Parse the output of new CMake versions.

As of CMake 3.0, the output of `cmake --version` now has a second line
showing that it is maintained by Kitware. Change the version parsing to
look only at the first line of output.

Change-Id: I347de4c376e0bde25a43a38d59587d9b63f6b43a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>