title: Cannot run `setup.py build` for mpi4py using PyPy
body: <p>I've been using the mpi4py library with OpenMPI to develop distributed memory programs.  So far, I've just been using vanilla Python 2.7 (CPython).</p>
  
  <p>According to the <a href="https://bitbucket.org/mpi4py/mpi4py" rel="nofollow">mpi4py project page</a>, mpi4py is compatible with "PyPy 2.0 and above".  </p>
  
  <p>On my installation of Fedora 22, I installed PyPy 2.4.0 with:</p>
  
  <p><code>sudo dnf install pypy pypy-devel</code></p>
  
  <p>Then I created a virtualenv and activated it with:</p>
  
  <p><code>virtualenv env -p $(which pypy) &amp;&amp; . env/bin/activate</code></p>
  
  <p>I then tried to install mpi4py with pip:</p>
  
  <p><code>pip install mpi4py</code></p>
  
  <p>But I get the following error:</p>
  
  <pre><code>...
  File "conf/mpidistutils.py", line 121, in customize_compiler
     cxx = cxx .replace('-pthread', '')
  AttributeError: 'NoneType' object has no attribute 'replace'
  </code></pre>
  
  <p>However, this same set of steps works just fine when using regular CPython.  I'm not terribly familiar with the nuances of PyPy; am I missing something obvious here?</p>
  
  <p>(Note:  I already had installed OpenMPI with <code>sudo dnf -y install openmpi openmpi-devel</code> on F22)</p>