Error while installing Nokogiri (1.6.7) on El Capitan
<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>