title: Does changing f(mystruct *a) to f(const mystruct *a) breaks API/ABI in C?
body: <pre><code>1: void f(mystruct *a)
  2: void f(const mystruct *a)
  </code></pre>
  
  <p>Does changing the function signature from 1->2 break API/ABI in C?<br>
  How about changing 2->1?</p>