Report skipped tests to cmake/ctest (#2429)

Report skipped tests to cmake/ctest (#2429)

This plumbing is required for cmake/ctest to recognise and report
skipped tests.

Now skipped tests in cmake ci jobs are reported like so:
```
          Start   7: libarchive_test_acl_platform_posix1e_read
    7/785 Test   #7: libarchive_test_acl_platform_posix1e_read ................................***Skipped   0.02 sec
```

And there is a list of skipped tests shown at the end of the test run.