title: Building Python3.7.3 from source missing '_ctypes'
body: <p>I'm trying to build Python-3.7.3 from source with <code>ensurepip</code> but i'm getting this error:</p>
  
  <pre><code>ModuleNotFoundError: No module named '_ctypes'
  </code></pre>
  
  <p>All of the answers online say that <code>libffi-dev</code> is needed but I have it installed and it still giving me this error.</p>
  
  <pre><code>root@4b6d672f1334:/Python-3.7.3# find / -name libffi.*
  /usr/lib/pkgconfig/libffi.pc
  /usr/lib/libffi.a
  /usr/lib/libffi.so
  /usr/lib/libffi.so.5.0.10
  /usr/lib/libffi.so.5
  /usr/share/info/libffi.info.gz
  </code></pre>
  
  <p>The build is in a container image from <code>ubuntu:10.04</code>.
  It is that old on purpose because I'm using PyInstaller to compile the application and it needs to run on machines with an old glibc (2.11) and this image is the only one that I could find that have this old version.</p>
  
  <p>I have done the same for Python-2.7.16 and it worked without any issues.</p>
  
  <p><strong>Update</strong>
  Python-3.6.8 is working without any issues as well</p>