Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

ruby

railsを触ってみようと思い
$ rails new [project name]
$ cd [project name]
$ sudo bundle update
とすると



Gem::Installer::ExtensionBuildError: 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

An error occurred while installing json (1.8.1), and Bundler cannot continue.

Make sure that `gem install json -v '1.8.1'` succeeds before bundling.
というエラーがでる。

色々調べた結果、
$ sudo ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future bundle update
$ sudo ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future bundle install
として完了させる。