CMP0057
-------

Support new :command:`if` IN_LIST operator.

CMake 3.3 adds support for the new IN_LIST operator.

The ``OLD`` behavior for this policy is to ignore the IN_LIST operator.
The ``NEW`` behavior is to interpret the IN_LIST operator.

This policy was introduced in CMake version 3.3.
CMake version |release| warns when the policy is not set and uses
``OLD`` behavior.  Use the :command:`cmake_policy` command to set
it to ``OLD`` or ``NEW`` explicitly.
