title: CMake convert date format
body: <p>I'm in the process of converting a configure script to a cmake system. HOwever i have run into an apparent brick wall with a particular line:</p>
  
  <pre><code>COMMIT_DATE=$(date +"%Y%m%d-%H%M" -ud "$(LC_ALL=C svn info | grep 'Changed Date' | cut -c20-45)")
  </code></pre>
  
  <p>How can format a date in cmake? Or assuming that i can't, what's the best, cross-platform way to do this? Obviously, this configure script currently only works on linux, however i would like the solution to be as cross-platform as possible.</p>
  
  <p>The svn part can be done relatively easily, so that doesn't need worrying about, other than the date input string is: (e.g.) "2013-10-14 21:55:05 +0100"</p>