AtlasCMake: declare atlas_add_library targets as non-system
ATLAS libraries, even when imported by child projects like WorkDir, should always be considered as non-system. Explicitly set the relevant properties on the library target and make sure to copy these properties on import.
This replaces the previously used global setting and requires cmake >= 3.25.
Closes ATLINFR-5446 and ATLINFR-5595.
Edited by Frank Winklmeier