CMAKE_POLICY_VERSION_MINIMUM

在 4.0 版被加入.

This is a CMake Environment Variable. Its initial value is taken from the calling process environment.

The default value for CMAKE_POLICY_VERSION_MINIMUM when there is no explicit configuration given on the first run while creating a new build tree. On later runs in an existing build tree the value persists in the cache as CMAKE_POLICY_VERSION_MINIMUM.