CMP0027
-------

Conditionally linked imported targets with missing include directories.

CMake 2.8.11 introduced introduced the concept of
INTERFACE_INCLUDE_DIRECTORIES, and a check at cmake time that the
entries in the INTERFACE_INCLUDE_DIRECTORIES of an IMPORTED target
actually exist.  CMake 2.8.11 also introduced generator expression
support in the target_link_libraries command.  However, if an imported
target is linked as a result of a generator expression evaluation, the
entries in the INTERFACE_INCLUDE_DIRECTORIES of that target were not
checked for existence as they should be.

The OLD behavior of this policy is to report a warning if an entry in
the INTERFACE_INCLUDE_DIRECTORIES of a generator-expression
conditionally linked IMPORTED target does not exist.

The NEW behavior of this policy is to report an error if an entry in
the INTERFACE_INCLUDE_DIRECTORIES of a generator-expression
conditionally linked IMPORTED target does not exist.

This policy was introduced in CMake version 3.0.  CMake version
|release| warns when the policy is not set and uses OLD behavior.  Use
the cmake_policy command to set it to OLD or NEW explicitly.