[Rails]Mac OS X El Capitan(10.11.4)でtherubyracerが入らなくなって泣きそうになったけど、なんとか解決した話

これが解決なのかどうか不安でたまらないけど、とりあえず動くので開発はこれでいいの、、かな？
## 条件
- Mac OS X El Capitan
    - バージョン10.11.4（15E65）
    - x86_64-darwin-15
        - `ruby -rubygems -e 'puts Gem::Platform.new(RUBY_PLATFORM)'`
- ruby2.3.0
    - rbenv

## 現象
```
Installing therubyracer 0.12.2 with native extensions

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    current directory: /Users/withelmo/xxxxx/vendor/bundle/ruby/2.3.0/gems/therubyracer-0.12.2/ext/v8
/Users/withelmo/.rbenv/versions/2.3.0/bin/ruby -r ./siteconf20160322-81622-1f6lzl1.rb extconf.rb --with-v8-dir
checking for main() in -lpthread... yes
checking for main() in -lobjc... yes
*** 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=/Users/withelmo/.rbenv/versions/2.3.0/bin/$(RUBY_BASE_NAME)
        --with-pthreadlib
        --without-pthreadlib
        --with-objclib
        --without-objclib
        --enable-debug
        --disable-debug
        --with-v8-dir
/Users/withelmo/.rbenv/versions/2.3.0/lib/ruby/2.3.0/mkmf.rb:1733:in `dir_config': undefined method `split' for true:TrueClass (NoMethodError)
        from /Users/withelmo/xxxxx/vendor/bundle/ruby/2.3.0/gems/libv8-3.16.14.13/ext/libv8/location.rb:49:in `configure'
        from /Users/withelmo/xxxxx/vendor/bundle/ruby/2.3.0/gems/libv8-3.16.14.13/lib/libv8.rb:7:in `configure_makefile'
        from extconf.rb:32:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Users/withelmo/xxxxx/vendor/bundle/ruby/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/therubyracer-0.12.2/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Users/withelmo/xxxxx/vendor/bundle/ruby/2.3.0/gems/therubyracer-0.12.2 for inspection.
Results logged to /Users/withelmo/xxxxx/vendor/bundle/ruby/2.3.0/extensions/x86_64-darwin-15/2.3.0-static/therubyracer-0.12.2/gem_make.out
```

## 対策
```
gem install libv8 -v '3.16.14.11' -- --with-system-v8
```

```
brew tap homebrew/versions
brew install v8-315
```

```
#.bundle/config
BUNDLE_BUILD__THERUBYRACER: "--with-v8-dir=/usr/local/opt/v8-315"
```

```
bundle install
```

## あとがき
毎回、 `therubyracer` と `nokogiri` には手を焼いている気がする
同じような誰かの参考に、役に立てられれば幸いです
この方法で解決しない場合もあるんではないかと

その場合は以下の記事を参考にいろいろ試していくしかない、のか？
- http://qiita.com/ganta/items/53f616b48e94d989952f
- http://qiita.com/puzzel/items/78638944ec2b0ffccb1b
- http://qiita.com/yakiimo23/items/eaf48164821897e3dde9
- http://qiita.com/akm/items/02c104fc3d39d68f96c7
- http://charlie23.hatenablog.jp/entry/2015/10/16/002055
- https://github.com/cowboyd/therubyracer/issues/359
- http://qiita.com/windhorn/items/394c10dea23d1e829cd1
 - http://qiita.com/yohawing/items/9d3ecfd2904692ed0e05
- http://qiita.com/ooyabuh/items/32e7086917e29356b532
- http://qiita.com/chrischris0801/items/eb78fabdbaece22b3662