In commit v3.9.0-rc1~55^2 (Improve Doxygen support, 2017-04-10)
use of the `IN_LIST` condition was added, but this is only supported
when policy CMP0057 is set to NEW.  Add a policy scope around the
module and enable the policy within it.  Otherwise it works only
in projects that happen to enable the policy.

Fixes: #18361