title: Error installing bcrypt with pip on OS X: can't find ffi.h (libffi is installed)
body: <p>I'm getting this error when trying to install bcrypt with pip. I have libffi installed in a couple places (the Xcode OS X SDK, and from homebrew), but I don't know how to tell pip to look for it. Any suggestions?</p>
  
  <pre><code>Downloading/unpacking bcrypt==1.0.2 (from -r requirements.txt (line 41))
    Running setup.py egg_info for package bcrypt
      OS/X: confusion between 'cc' versus 'gcc' (see issue 123)
      will not use '__thread' in the C code
      c/_cffi_backend.c:14:10: fatal error: 'ffi.h' file not found
      #include &lt;ffi.h&gt;
               ^
      1 error generated.
      Traceback (most recent call last):
        File "&lt;string&gt;", line 16, in &lt;module&gt;
        File "/Users/cody/virtualenvs/analytics/build/bcrypt/setup.py", line 104, in &lt;module&gt;
          "Programming Language :: Python :: 3.3",
        File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 112, in setup
          _setup_distribution = dist = klass(attrs)
        File "build/bdist.macosx-10.9-intel/egg/setuptools/dist.py", line 239, in __init__
        File "build/bdist.macosx-10.9-intel/egg/setuptools/dist.py", line 264, in fetch_build_eggs
        File "build/bdist.macosx-10.9-intel/egg/pkg_resources.py", line 620, in resolve
          dist = best[req.key] = env.best_match(req, ws, installer)
        File "build/bdist.macosx-10.9-intel/egg/pkg_resources.py", line 858, in best_match
          return self.obtain(req, installer) # try and download/install
        File "build/bdist.macosx-10.9-intel/egg/pkg_resources.py", line 870, in obtain
          return installer(requirement)
        File "build/bdist.macosx-10.9-intel/egg/setuptools/dist.py", line 314, in fetch_build_egg
        File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 593, in easy_install
  
        File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 623, in install_item
  
        File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 811, in install_eggs
  
        File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 1017, in build_and_install
  
        File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 1005, in run_setup
  
      distutils.errors.DistutilsError: Setup script exited with error: command 'cc' failed with exit status 1
      Complete output from command python setup.py egg_info:
      OS/X: confusion between 'cc' versus 'gcc' (see issue 123)
  
  will not use '__thread' in the C code
  
  c/_cffi_backend.c:14:10: fatal error: 'ffi.h' file not found
  
  #include &lt;ffi.h&gt;
  
           ^
  
  1 error generated.
  
  Traceback (most recent call last):
  
    File "&lt;string&gt;", line 16, in &lt;module&gt;
  
    File "/Users/cody/virtualenvs/analytics/build/bcrypt/setup.py", line 104, in &lt;module&gt;
  
      "Programming Language :: Python :: 3.3",
  
    File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 112, in setup
  
      _setup_distribution = dist = klass(attrs)
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/dist.py", line 239, in __init__
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/dist.py", line 264, in fetch_build_eggs
  
    File "build/bdist.macosx-10.9-intel/egg/pkg_resources.py", line 620, in resolve
  
      dist = best[req.key] = env.best_match(req, ws, installer)
  
    File "build/bdist.macosx-10.9-intel/egg/pkg_resources.py", line 858, in best_match
  
      return self.obtain(req, installer) # try and download/install
  
    File "build/bdist.macosx-10.9-intel/egg/pkg_resources.py", line 870, in obtain
  
      return installer(requirement)
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/dist.py", line 314, in fetch_build_egg
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 593, in easy_install
  
  
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 623, in install_item
  
  
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 811, in install_eggs
  
  
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 1017, in build_and_install
  
  
  
    File "build/bdist.macosx-10.9-intel/egg/setuptools/command/easy_install.py", line 1005, in run_setup
  
  
  
  distutils.errors.DistutilsError: Setup script exited with error: command 'cc' failed with exit status 1
  
  ----------------------------------------
  Command python setup.py egg_info failed with error code 1 in /Users/cody/virtualenvs/analytics/build/bcrypt
  </code></pre>