title: How to check Linux version with Autoconf?
body: <p>My program requires at least Linux 2.6.26 (I use timerfd and some other Linux-specific features).</p>
  
  <p>I have an general idea how to write this macro but I don't have enough knowledge about writing  test macros for Autoconf. Algorithm:</p>
  
  <ol>
  <li>Run "uname --release" and store output</li>
  <li>Parse output and subtract Linux version number (MAJOR.MINOR.MICRO)</li>
  <li>Compare version</li>
  </ol>
  
  <p>I don't know how to run command, store output and parse it.</p>
  
  <p>Maybe such macro already exists and it's available (I haven't found any)? </p>