[Ruby] Error trying to install ffi gem

ffi

When attempting to install ffi gem:

$ gem install ffi
Building native extensions.  This could take a while...
ERROR:  Error installing ffi:
	ERROR: Failed to build gem native extension.

        /Users/fc/.rvm/rubies/ruby-1.9.2-p290/bin/ruby extconf.rb
checking for ffi.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

When attempting to compile ffi from source (https://github.com/ffi/ffi):

$ rake gem:install
rake-compiler must be configured first to enable cross-compilation
rake-compiler must be configured first to enable cross-compilation
rake/rdoctask is deprecated.  Use rdoc/task instead (in RDoc 2.4.2+)
[warn] YARD unavailable
  Successfully built RubyGem
  Name: ffi
  Version: 1.0.10
  File: ffi-1.0.10.gem
mv ffi-1.0.10.gem ../ffi-1.0.10.gem
sudo gem install --local pkg/ffi-1.0.10
Building native extensions.  This could take a while...
ERROR:  Error installing pkg/ffi-1.0.10:
	ERROR: Failed to build gem native extension.

        /Users/fc/.rvm/rubies/ruby-1.9.2-p290/bin/ruby extconf.rb
checking for ffi.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Both done on Mac OS X 10.7.2 using Ruby v1.9.2-p290. Xcode 4.2 is installed.

http://comments.gmane.org/gmane.comp.lang.ruby.ffi/67