The intended license for the CMake modules is BSD-2-Clause;
there's no desire to restrict what can be done with these,
and CMake modules are generally 2-clause licensed.
- The auto-generated code produces a lot of warnings from
Clang 8; this obscures the more meaningful warnings from
actual Calamares code, so tone the warnings down.
- For Clang, set CALAMARES_MOC_OPTIONS.
- Add convenience CMake function for automoccing. It applies
the options as needed to a given target.
