title: Make: only build something if the source's md5 checksum was changed
body: <p>Is it possible to tell <code>make</code> to only build a target if it's sources md5 checksum has changed (instead of the edit time)?</p>
  
  <p>I'm using <code>make</code> to compile my <code>.tex</code> files and I need to prevent it from building everything twice all the time.</p>
  
  <p>I've tried using Scons, but I feel this isn't adaptable to other needs I have. </p>