title: rails 5.0.0 when installing "nio4r" : Failed to build gem native extension
body: <p>Here is the logs: <a href="http://pastebin.com/CAgur9xd" rel="noreferrer">http://pastebin.com/CAgur9xd</a></p>
  
  <pre><code>Installing nio4r 1.2.1 with native extensions
  
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  
      C:/RailsInstaller/Ruby2.2.0/bin/ruby.exe -r ./siteconf20160720-8272-c88sgk.rb extconf.rb --with-cflags=-std=c99
  checking for unistd.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
          --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=C:/RailsInstaller/Ruby2.2.0/bin/$(RUBY_BASE_NAME)
  C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:456:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
  You have to install development tools first.
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:587:in `try_cpp'
           from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:1060:in `block in have_header'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:911:in `block in checking_for'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:351:in `block (2 levels) in postpone'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:321:in `open'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:351:in `block in postpone'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:321:in `open'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:347:in `postpone'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:910:in `checking_for'
          from C:/RailsInstaller/Ruby2.2.0/lib/ruby/2.2.0/mkmf.rb:1059:in `have_header'
          from extconf.rb:3:in `&lt;main&gt;'
  
  extconf failed, exit code 1
  </code></pre>
  
  <p>when installing bundle it returns(starts at line 117 in the logs ):</p>
  
  <pre><code>Installing nio4r 1.2.1 with native extensions
  Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
  </code></pre>
  
  <p>So the bundle can't be installed. It returns at the end :</p>
  
  <pre><code>An error occurred while installing nio4r (1.2.1), and Bundler cannot continue.
  Make sure that `gem install nio4r -v '1.2.1'` succeeds before bundling.
  </code></pre>
  
  <p>Note :I have tried the solutions in other questions, but it is still the same.
  If it is possible to install "nio4r" manually please tell me how .</p>