Previously there was a variable CGAL_SHARED_LIBS defined by
CGALConfig.cmake. This one is now unified with CGAL_BUILD_SHARED_LIBS.
And the option CGAL_BUILD_SHARED_LIBS is only defined as an option if one
are building CGAL libraries. If CGAL_Common.cmake is included from another
project, such as from UseCGAL.cmake, then this variable is set in
CGALConfig.cmake as a regular (non-cached) CMake variable.
We declare
cmake_minimum_required(VERSION 2.6.2)
but we also use
cmake_policy(VERSION 2.8.4)
to declare that our CMake scripts are OK with all the defaults of CMake policies
as of CMake-2.8.4. That shuts down the warnings of CMake-2.8.4.
That way, we no longer need any declaration of specific policies.