title: Print check_cxx_source_runs() detailed output
body: <p>I have a find package module that utilizes <code>check_cxx_source_runs()</code> to test if package was loaded properly. However, it fails and I am not sure what causes it to.</p>
  <p>Is there any way I can print the actual error (as one would see on terminal) from <code>check_cxx_source_runs()</code> rather than just the variable that tells success/failure?</p>