Disallow include export result.
CMake 2.8.12 and lower allowed use of the include() command with the result of the export() command. This relies on the assumption that the export() command has an immediate effect at configure-time during a cmake run. Certain properties of targets are not fully determined until later at generate-time, such as the link language and complete list of link libraries. Future refactoring will change the effect of the export() command to be executed at generate-time. Use ALIAS targets instead in cases where the goal is to refer to targets by another name.
The OLD behavior for this policy is to allow including the result of an export() command. The NEW behavior for this policy is not to allow including the result of an export() command.
This policy was introduced in CMake version 3.0. CMake version 3.7.1 warns when the policy is not set and uses OLD behavior. Use the cmake_policy command to set it to OLD or NEW explicitly.
OLD behavior of a policy is
deprecated by definition
and may be removed in a future version of CMake.