title: What does x mean before precompiled header(expecting ! - exclamation point)?
body: <p>I've been trying to use precompiled headers mentioned here:  <a href="https://stackoverflow.com/questions/58841/precompiled-headers-with-gcc">Precompiled headers with GCC</a></p>
  
  <p>But after compiling my precompiled header file.h.gch, when I compile other files that include file.h with the -H option, instead of seeing </p>
  
  <pre><code>! /my/precompiled/header/file.h.gch
  </code></pre>
  
  <p>I'm seeing </p>
  
  <pre><code>x /my/precompiled/header/file.h.gch
  </code></pre>
  
  <p>Any idea what this means? The <a href="https://gcc.gnu.org/onlinedocs/gcc/Precompiled-Headers.html" rel="nofollow noreferrer">documentation</a> doesn't mention either(! or x ).</p>