I get this gem installation error for kgio gem when I do the package installation

I added a unicorn to my Gemfile, and after that, when I install the package, I get this error

    em::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/bin/ruby extconf.rb 
checking for CLOCK_MONOTONIC in time.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/adim86/.rvm/rubies/ruby-1.9.3-p0/bin/ruby
/Users/adim86/.rvm/rubies/ruby-1.9.3-p0/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/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:491:in `block in try_compile'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:443:in `with_werror'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:491:in `try_compile'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:686:in `macro_defined?'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:822:in `block in have_macro'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:254:in `open'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:254:in `open'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
    from /Users/adim86/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/mkmf.rb:821:in `have_macro'
    from extconf.rb:5:in `<main>'


Gem files will remain installed in /Users/adim86/.rvm/gems/ruby-1.9.3-p0/gems/kgio-2.7.4 for inspection.
Results logged to /Users/adim86/.rvm/gems/ruby-1.9.3-p0/gems/kgio-2.7.4/ext/kgio/gem_make.out
An error occured while installing kgio (2.7.4), and Bundler cannot continue.
Make sure that `gem install kgio -v '2.7.4'` succeeds before bundling

My gem file looks like this. I tried adding a unicorn to the production block, but I still get the same error. I also deleted the unicorn and I still get the same error, also tried updating the package to no avail:

source 'https://rubygems.org'

gem 'rails', '3.2.3'

gem 'devise'
gem 'haml-rails'

gem 'omniauth'
gem 'omniauth-twitter'
gem 'omniauth-facebook'
gem 'twitter'
gem 'fb_graph'

gem 'json'
gem 'json_pure'

gem 'simple_form'
gem 'postmark'
gem 'postmark-rails'

gem 'bootstrap-datepicker-rails'
gem 'watu_table_builder', :require => 'table_builder'

gem 'sqlite3'

# Gems used only for assets and not required
# in production environments by default.
group :assets do
  gem 'uglifier', '>= 1.0.3'
end

gem "therubyracer", :require => 'v8'

gem 'jquery-rails'

gem 'differ'


gem 'whenever'
gem 'unicorn'

can anyone help?