CMP0021ΒΆ
Fatal error on relative paths in INCLUDE_DIRECTORIES target
property.
CMake 2.8.10.2 and lower allowed the INCLUDE_DIRECTORIES target
property to contain relative paths. The base path for such relative
entries is not well defined. CMake 2.8.12 issues a FATAL_ERROR if the
INCLUDE_DIRECTORIES property contains a relative path.
The OLD behavior for this policy is not to warn about relative paths
in the INCLUDE_DIRECTORIES target property. The NEW behavior for this
policy is to issue a FATAL_ERROR if INCLUDE_DIRECTORIES contains a
relative path.
This policy was introduced in CMake version 2.8.12. CMake version
3.18.6 warns when the policy is not set and uses OLD behavior. Use
the cmake_policy() command to set it to OLD or NEW explicitly.
Note
The OLD behavior of a policy is
deprecated by definition
and may be removed in a future version of CMake.