ruby – 在cygwin上安装webdriver gem时出错

“gem install selenium-webdriver-2.26.0.gem”:(注意我想使用Ruby在Cygwin下安装Webdriver gem).

$gem install selenium-webdriver-2.26.0.gem
Building native extensions.  This could take a while... 
ERROR:  Error installing selenium-webdriver-2.26.0.gem:
ERROR: Failed to build gem native extension.


/usr/bin/ruby.exe extconf.rb checking for ffi.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=/usr/bin/ruby
        --with-ffi_c-dir
        --without-ffi_c-dir
        --with-ffi_c-include
        --without-ffi_c-include=${ffi_c-dir}/include
        --with-ffi_c-lib
        --without-ffi_c-lib=${ffi_c-dir}/lib
        --with-libffi-config
        --without-libffi-config
        --with-pkg-config
        --without-pkg-config 
     /usr/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an  executable file.
(RuntimeError) You have to install development tools first.
        from /usr/lib/ruby/1.9.1/mkmf.rb:506:in `try_cpp'
        from /usr/lib/ruby/1.9.1/mkmf.rb:931:in `block in have_header'
        from /usr/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
        from /usr/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
        from /usr/lib/ruby/1.9.1/mkmf.rb:254:in `open'
        from /usr/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
        from /usr/lib/ruby/1.9.1/mkmf.rb:254:in `open'
        from /usr/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
        from /usr/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
        from /usr/lib/ruby/1.9.1/mkmf.rb:930:in `have_header'
        from extconf.rb:14:in `<main>'


Gem files will remain installed in
/usr/lib/ruby/gems/1.9.1/gems/ffi-1.2.0 for inspection. Results
logged to
/usr/lib/ruby/gems/1.9.1/gems/ffi-1.2.0/ext/ffi_c/gem_make.out

请指导我解决这个问题需要做些什么？任何帮助深表感谢.