title: Installing therubyracer at heroku, failed to build gem native extension
body: <p>I keep having error uploading the Rails app to Heroku</p>
  
  <pre><code>Installing therubyracer (0.11.0)
         Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.
         /usr/local/bin/ruby extconf.rb
         checking for main() in -lpthread... yes
         checking for v8.h... no
         *** 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=/usr/local/bin/ruby
         --with-pthreadlib
         --without-pthreadlib
         --enable-debug
         --disable-debug
         --with-v8-dir
         --without-v8-dir
         --with-v8-include
         --without-v8-include=${v8-dir}/include
         --with-v8-lib
         --without-v8-lib=${v8-dir}/lib
         /tmp/build_3srt9ifqtbs6m/vendor/bundle/ruby/1.9.1/gems/therubyracer-0.11.0/ext/v8/build.rb:42:in `build_with_system_libv8': unable to locate libv8. Please see output for details (RuntimeError)
         from extconf.rb:22:in `&lt;main&gt;'
         The Ruby Racer requires libv8 ~&gt; 3.11.8
         to be present on your system in order to compile
         and link, but it could not be found.
         In order to resolve this, you will either need to manually
         install an appropriate libv8 and make sure that this
         build process can find it. If you install it into the
         standard system path, then it should just be picked up
         automatically. Otherwise, you'll have to pass some extra
         flags to the build process as a hint.
         If you don't want to bother with all that, there is a
         rubygem that will do all this for you. You can add
         following line to your Gemfile:
         gem 'libv8', '~&gt; 3.11.8'
         We hope that helps, and we apologize, but now we have
         to push the eject button on this install.
         thanks,
         The Mgmt.
         Gem files will remain installed in /tmp/build_3srt9ifqtbs6m/vendor/bundle/ruby/1.9.1/gems/therubyracer-0.11.0 for inspection.
         Results logged to /tmp/build_3srt9ifqtbs6m/vendor/bundle/ruby/1.9.1/gems/therubyracer-0.11.0/ext/v8/gem_make.out
         An error occurred while installing therubyracer (0.11.0), and Bundler cannot continue.
         Make sure that `gem install therubyracer -v '0.11.0'` succeeds before bundling.
   !
   !     Failed to install gems via Bundler.
   !
   !     Heroku push rejected, failed to compile Ruby/rails app
  </code></pre>
  
  <p>the part of the Gem file</p>
  
  <pre><code>gem 'libv8', '~&gt; 3.11.8'
  gem "therubyracer", :platforms =&gt; :ruby, :require =&gt; 'v8'
  group :linux_test do
    #gem "therubyracer", :require =&gt; false
    gem "libnotify", :require =&gt; false
  end
  group :production do
    gem "therubyracer-heroku"
    gem "pg"
  end
  </code></pre>
  
  <p><code>therubyracer</code> and <code>lib8</code> is up to date for sure, I reinstalled them just now.</p>
  
  <p>How do I fix it?</p>
  
  <p>P.S. Ubuntu 12.1, x64.</p>