Mutex on hash table for cffi-libffi
Mutex on hash table for cffi-libffi

Use Bordeaux threads to thread lock access to the hash table, to make
compilation thread safe. There probably isn't much risk of conflict in
practice, but if Bordeaux threads is installed, this should remove that
risk.  Closes https://bugs.launchpad.net/cffi/+bug/1474211.

stassats/cffi,3b/cffi,attila-lendvai/cffi,stassats/cffi,cffi/cffi,mcna/cffi,dkochmanski/cffi,3b/cffi,stassats/cffi,dkochmanski/cffi,dkochmanski/cffi,mcna/cffi,3b/cffi,cffi/cffi,cffi/cffi,attila-lendvai/cffi