title: GLib compile error (ffi.h), but libffi is installed
body: <p>After a succesful configure, make exits with <em>snipped</em></p>
  
  <pre><code>gclosure.c:29:17: fatal error: ffi.h: No such file or directory
  compilation terminated.
  </code></pre>
  
  <p>I have libffi installed, and locate ffi.h gives:</p>
  
  <pre><code>/home/luca/gcc4.6/gcc-4.6.0/libffi/include/ffi.h.in
  /usr/include/x86_64-linux-gnu/ffi.h
  /usr/share/doc/ghc-doc/html/users_guide/ffi.html
  /usr/share/doc/libffi5/html/Using-libffi.html
  </code></pre>