`luarocks install alien` on OS X with Homebrew
If you just do luarocks install alien you may get this error:
checking for ffi_closure_alloc in -lffi... no configure: error: in `/tmp/luarocks_alien-0.7.0-1-1080/alien-0.7.0': configure: error: cannot find new enough libffi
The solution is to specify the lib directory with CFLAGS:
brew install libffi CFLAGS='-L/usr/local/opt/libffi/lib' luarocks install alien