title: Error while installing Nokogiri (1.6.7) on El Capitan
body: <p>One of my developers have updated Nokogiri, and when pulling the updated Gemfile my <code>bundle install</code> fails.</p>
  
  <pre><code>➜  my-project git:(master) bundle install
  Fetching source index from https://rubygems.org/
  Using rake 10.4.2
  Using i18n 0.7.0
  Using json 1.8.3
  Using minitest 5.8.3
  Using thread_safe 0.3.5
  Using tzinfo 1.2.2
  Using activesupport 4.2.3
  Using builder 3.2.2
  Using erubis 2.7.0
  Using mini_portile2 2.0.0
  
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  
      /Users/me/.rvm/rubies/ruby-2.1.2/bin/ruby extconf.rb --use-system-libraries
  checking if the C compiler accepts ... yes
  checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
  Building nokogiri using system libraries.
  libxml2 version 2.6.21 or later is required!
  *** 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/me/.rvm/rubies/ruby-2.1.2/bin/ruby
    --help
    --clean
    --use-system-libraries
    --with-zlib-dir
    --without-zlib-dir
    --with-zlib-include
    --without-zlib-include=${zlib-dir}/include
    --with-zlib-lib
    --without-zlib-lib=${zlib-dir}/lib
    --with-xml2-dir
    --without-xml2-dir
    --with-xml2-include
    --without-xml2-include=${xml2-dir}/include
    --with-xml2-lib
    --without-xml2-lib=${xml2-dir}/lib
    --with-libxml-2.0-config
    --without-libxml-2.0-config
    --with-pkg-config
    --without-pkg-config
    --with-xslt-dir
    --without-xslt-dir
    --with-xslt-include
    --without-xslt-include=${xslt-dir}/include
    --with-xslt-lib
    --without-xslt-lib=${xslt-dir}/lib
    --with-libxslt-config
    --without-libxslt-config
    --with-exslt-dir
    --without-exslt-dir
    --with-exslt-include
    --without-exslt-include=${exslt-dir}/include
    --with-exslt-lib
    --without-exslt-lib=${exslt-dir}/lib
    --with-libexslt-config
    --without-libexslt-config
  
  extconf failed, exit code 1
  
  Gem files will remain installed in /Users/me/.rvm/gems/ruby-2.1.2@my-project/gems/nokogiri-1.6.7 for inspection.
  Results logged to /Users/me/.rvm/gems/ruby-2.1.2@my-project/extensions/x86_64-darwin-13/2.1.0-static/nokogiri-1.6.7/gem_make.out
  An error occurred while installing nokogiri (1.6.7), and Bundler cannot continue.
  Make sure that `gem install nokogiri -v '1.6.7'` succeeds before bundling.
  </code></pre>
  
  <p>As suggested in "<a href="https://stackoverflow.com/questions/27496498/failing-to-install-nokogiri-gem/27696382#27696382">Failing to install Nokogiri gem</a>" I have unsuccessfully tried to run:</p>
  
  <pre><code>bundle config build.nokogiri --use-system-libraries
  bundle install
  </code></pre>
  
  <p>As suggested in "<a href="https://stackoverflow.com/questions/27496498/failing-to-install-nokogiri-gem/27496640#27496640">Failing to install Nokogiri gem</a>" I also tried:</p>
  
  <pre><code>gem install nokogiri -- --use-system-libraries
  </code></pre>
  
  <p>and:</p>
  
  <pre><code>gem install nokogiri -v 1.6.5 -- --use-system-libraries
  </code></pre>
  
  <p>My OS version is El Capitan 10.11.2, and I have checked that the Xcode licence agreement has been accepted.</p>
  
  <p>Any ideas how to get the Nokogiri installation to succeed?</p>