title: How to full expand variables in autoconf?
body: <p>In this example: </p>
  
  <pre><code>configure.ac: 
    ...
    AC_CONFIG_FILES([script1])
    AC_OUTPUT
  
  script1.in: 
    #!/bin/bash
    ...
    config=@datadir@/blah
  </code></pre>
  
  <p>This <code>@datadir@</code> is expanded to <code>${prefix}/share</code>, is there any way to expand it to <code>/usr/local/share</code>?</p>