title: CMake system include search path
body: <p>I'm wondering how I would go about adding an include directory to the system search path for a CMake project. Particularly, I've some source that I'm trying to build a CMake project for.</p>
  
  <p>The source is not mine, and so I don't really want to modify it.</p>
  
  <p>The source has the following include directive:</p>
  
  <pre><code>#include &lt;foo/bar.h&gt;
  </code></pre>
  
  <p>So I need to add the directory containing foo to my search path. Is this something I can set within the CMakeLists.txt?</p>