274e09cd introduced a skip of the generation if the target file is not
present. While this might hint a wrong target directory it also prevents the
generation of new files. Since the provided mesa_pd.py script asks to
confirm the target directory anyway, this skip is removed.

Since some benchmarks/tutorials are registered as tests they have to be
built in order to run.

use cuda as a first level language in CMake with `enable_language(CUDA)`
enable tests where cuda and codegen are both activated
various minor fixes