title: include header files in cmake
body: <p>I have a CMakeList.txt file which has just one liner
  <code>include(startevn.cmake)</code>
  in startevn.cmake I have, </p>
  
  <pre><code>project(startevn)
  set(headers 
     startup.h
  )
  set(sources
    system-init.cpp
  )
  new_library(startevn ${sources} ${headers})
  </code></pre>
  
  <p>Now I have to move the startup to a different directory. After doing that I added
  the following line to "startevn.cmake",</p>
  
  <pre><code>include_directories("/new_folder_location/sub_folder")
  </code></pre>
  
  <p>where sub_folder is where startup.h is now located but compiler still says
  Cannot find source file: startup.h.
  What am I doing wrong?</p>