title: configure_file list of files -> #includes cmake
body: <p>This seems like something that should be easy to do, but I cant for the life of me figure out how to do it.</p>
  
  <p>Basically, I want to take a source lists (for now, just a variable ${HDR_LIST}), and write them ALL as includes in a file. so if <code>HDR_LIST="foo.h;bar.h;baz.h;quz.h"</code> it would make the file</p>
  
  <pre><code>#include "foo.h"
  #include "bar.h"
  #include "baz.h"
  #include "quz.h"
  </code></pre>
  
  <p>I'd like this file to only update if HDR_LIST changes.</p>
  
  <p>The only way I can think to do it is to make a configure_file command...but this macro may be in a ton of places. Each each project sets the variable, I'm not sure how safe that is. I feel like there should be a better way...</p>