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

        /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/bin/ruby extconf.rb
checking for asprintf()... *** 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
	--without-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/adrian/.rvm/rubies/ruby-1.9.2-p290/bin/ruby
/Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:368:in `try_do': The complier failed to generate an executable file. (RuntimeError)
You have to install development tools first.
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:435:in `try_link0'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:440:in `try_link'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:552:in `try_func'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:797:in `block in have_func'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:693:in `block in checking_for'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:280:in `block (2 levels) in postpone'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:254:in `open'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:280:in `block in postpone'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:254:in `open'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:276:in `postpone'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:692:in `checking_for'
	from /Users/adrian/.rvm/rubies/ruby-1.9.2-p290/lib/ruby/1.9.1/mkmf.rb:796:in `have_func'
	from extconf.rb:3:in `<main>'


Gem files will remain installed in /Users/adrian/.rvm/gems/ruby-1.9.2-p290@pluto/gems/bson_ext-1.6.4 for inspection.
Results logged to /Users/adrian/.rvm/gems/ruby-1.9.2-p290@pluto/gems/bson_ext-1.6.4/ext/cbson/gem_make.out