title: How to compile for legacy os
body: <p>I am using Cent OS 5. </p>
  
  <p>It has legacy package installed. </p>
  
  <p>With what version of gcc should I compile ?</p>
  
  <p>Does it really required to compile with old gcc version to support old linux os ?</p>
  
  <p>if yes why ?</p>