title: CMake : Include subdirectories
body: <p>I have currently, in my CMake lists :</p>
  
  <pre><code>FIND_PATH(BOINC_INCLUDE_DIR NAMES boinc_api.h
        PATH_SUFFIXES boinc
        DOC "The Boinc include directory (where boinc_api.h is)")
  </code></pre>
  
  <p>This command find the directory /usr/include/boinc.
  But I want to add all the subdirectories in the boinc directory.
  How to do that ?</p>
  
  <p>Thank you very much.</p>