cabal check should verify that the sdist, doesn't contain generated files

With #4874 we start running `configure` in the build directory instead of the source directory. As such if the source directory contains files that are also generated by the `configure` script, this used to result in overridden files. Now we end up with two copies of the files. In the case of header files this can now results in compilation issues.

As such cabal check should verify that generated files do not end up in the source tarball.

See also haskell/network#307

Start at the cabal check command and trace the sdist-generation path, with attention to how configure-generated files are recognized. Define the check around source tarballs and verify that a problematic sdist containing generated files is reported while a clean sdist passes.

Written by the indexing model from the issue text.