mac安装rails时，安装不上，报错。?报错

用brew，已经安装完了ruby，版本：ruby 2.0.0p247 (2013-06-27 revision 41674) [universal.x86_64-darwin13]

看网上的文档，说输入sudo gem install rails 就可以安装rails了。。可是我输入完，输完密码后，出现下面的信息。。肿么办？？求指教～！

Building native extensions.  This could take a while...

ERROR:  Error installing rails:
ERROR: Failed to build gem native extension.


    /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb
creating Makefile


make "DESTDIR="
compiling generator.c
linking shared-object json/ext/generator.bundle
clang: error: unknown argument: '-multiply_definedsuppress' [-Wunused-command-line-argument-hard-error-in-future]
clang: note: this will be a hard error (cannot be downgraded to a warning) in the future
make: *** [generator.bundle] Error 1




Gem files will remain installed in /Library/Ruby/Gems/2.0.0/gems/json-1.8.1 for inspection.
Results logged to /Library/Ruby/Gems/2.0.0/gems/json-1.8.1/ext/json/ext/generator/gem_make.out
1 gem installed