title: Gem therubyracer does not install even if libv8 is installed
body: <p>I have installed <code>libv8</code> gem on windows by using this command:</p>
  
  <pre><code>gem install libv8 -- --with-system-v8
  </code></pre>
  
  <p>Then when I try to install <code>therubyracer</code> it gives me long error message:</p>
  
  <pre><code>Installing therubyracer 0.12.2 with native extensions
  
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  
  current directory: D:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/therubyracer- 0.12.2/ext/v8
  D:/Ruby21-x64/bin/ruby.exe -r ./siteconf20160105-4924-101vdyd.rb 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=D:/Ruby21-x64/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
  D:/Ruby21-x64/lib/ruby/gems/2.1.0/gems/libv8-3.16.14.13/ext/libv8/location.rb:50:in `configure': You have chosen to use the version of V8 found on your system (Libv8::Location::System::NotFoundError)
  and *not* the one that is bundle with the libv8 rubygem. However,
  it could not be located. please make sure you have a version of
  v8 that is compatible with 3.16.14.13 installed. You may
  need to special --with-v8-dir options if it is in a non-standard
  location
  
  thanks,
  The Mgmt
  </code></pre>
  
  <p>What I understood is that therubyracer wants to find <code>v8</code>. I have installed Node.js which already has it. Is it even possible to use it? Or there are other solutions for therubyracer?</p>