title: build emacs and gnutls not found
body: <p>I built emacs26 on Ubuntu16.04, when I executed <code>./config --prefix=/usr/local/emacs</code> , it showed like this:</p>
  
  <pre><code>configure: error: The following required libraries were not found:
       gnutls
  Maybe some development libraries/packages are missing?
  If you don't want to link with them give
       --with-gnutls=no
  as options to configure
  </code></pre>
  
  <p>I tried to solve this problem many times, but failed. Who can help me, thank you very much.</p>