ffi fails

output.txt

✗ gem install ffi -v '1.1.5'
Building native extensions.  This could take a while...
ERROR:  Error installing ffi:
	ERROR: Failed to build gem native extension.

        /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/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.

Provided configuration options:
	--with-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/bin/ruby
	--with-ffi_c-dir
	--without-ffi_c-dir
	--with-ffi_c-include
	--without-ffi_c-include=${ffi_c-dir}/include
	--with-ffi_c-lib
	--without-ffi_c-lib=${ffi_c-dir}/lib
	--with-libffi-config
	--without-libffi-config
	--with-pkg-config
	--without-pkg-config
/Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:506:in `try_cpp'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:931:in `block in have_header'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:254:in `open'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:254:in `open'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
	from /Users/bartolsthoorn/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/1.9.1/mkmf.rb:930:in `have_header'
	from extconf.rb:9:in `<main>'


Gem files will remain installed in /Users/bartolsthoorn/.rvm/gems/ruby-1.9.3-p194/gems/ffi-1.1.5 for inspection.
Results logged to /Users/bartolsthoorn/.rvm/gems/ruby-1.9.3-p194/gems/ffi-1.1.5/ext/ffi_c/gem_make.out