title: build LXML. pre-compiled .c Cython files missing
body: <p>I must build lxml from source. <code>https://github.com/lxml/lxml</code>
  As the file <code>/doc/build.txt</code> says, source code should be provided with pre-compiled .c files. Why I don't find them?  in <code>/src/lxml</code> there are only .pyx files. Where .c files are??</p>
  
  <p>In fact I have the <code>lxml.etree.c</code> missing file during <code>python build</code> command.</p>
  
  <p>Thank you</p>