The CMake policy warnings at the end explicitly inform users that they should not concern themselves with the messages. The messages are there for the project developers.
CMake Warning (dev) at c/tools/CMakeLists.txt:22 (add_executable):
Policy CMP0069 is not set: INTERPROCEDURAL_OPTIMIZATION is enforced when
enabled. Run "cmake --help-policy CMP0069" for policy details. Use the
cmake_policy command to set the policy and suppress this warning.
INTERPROCEDURAL_OPTIMIZATION property will be ignored for target
This warning is for project developers. Use -Wno-dev to suppress it.
-Wno-dev to suppress it.
However, sometimes as a user of a software, you have a good reason to set a policy when you are installing the project. One reason might be to enable the link-time optimization (also called interprocedural optimization). Without setting a policy, CMake will ignore the
In such a case, you can use
-DCMAKE_POLICY_DEFAULT_CMP<NNNN> to get the behavior you need, without editing CMakeLists.txt. Of course, contacting the developer, suggesting that they deal with the policy in source, is a good practice.