ruby – 错误：无法在Yosemite上构建gem原生扩展

sudo gem install cocoapods

这是提到的命令的响应.

Building native extensions.  This could take a while...
ERROR:  Error installing cocoapods:
    ERROR: Failed to build gem native extension.

    "/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby" -rubygems /Library/Ruby/Gems/2.0.0/gems/rake-0.9.6/bin/rake RUBYARCHDIR=/Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/ext RUBYLIBDIR=/Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/ext
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
checking for -std=c99 option to compiler... *** 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=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:434:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:549:in `block in try_compile'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:502:in `with_werror'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:549:in `try_compile'
    from extconf.rb:24:in `block in <main>'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:895:in `block in checking_for'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:340:in `block (2 levels) in postpone'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:310:in `open'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:340:in `block in postpone'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:310:in `open'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:336:in `postpone'
    from /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/mkmf.rb:894:in `checking_for'
    from extconf.rb:23:in `<main>'
rake aborted!
Command failed with status (1): [/System/Library/Frameworks/Ruby.framework/...]
/Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/ext/xcodeproj/Rakefile:37:in `block in <top (required)>'
Tasks: TOP => default => ext
(See full trace by running task with --trace)


Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/gems/xcodeproj-0.17.0/ext/xcodeproj/gem_make.out

有人可以帮帮我吗？