title: How can I make cmake not to delete object files so that I could quickly change between debug/release?
body: <p>I frequently change between debug and release build of a large-ish library. Whenever I issue a </p>
  
  <pre><code>cmake . -DCMAKE_BUILD_TYPE=DEBUG
  </code></pre>
  
  <p>or the same with RELEASE and do a make, everything is recompiling. I'd like cmake to recompile only the files changed since I built last time with the given mode. Can I do that, and if so, how?</p>
  
  <p>I am using OSX and clang.</p>