title: Add library to Cmake project
body: <p>Perhaps I simply can't find it, but I want to add some code to a project of mine (libunwind found here <a href="http://www.nongnu.org/libunwind/download.html" rel="nofollow noreferrer">http://www.nongnu.org/libunwind/download.html</a>)<br>
  This library does not come with a CMakeLists.txt file and when I try to include it cmake complains about this fact. Right now I've simply added the libunwind directory to my external code and added a reference in my main CMakeLists.txt  </p>
  
  <p>Any input would be great.</p>