rmagick
Ref: http://qiita.com/hidechae/items/56e8cca8a77610aa0ab4
$ curl https://raw.githubusercontent.com/Homebrew/homebrew-core/f6b47796d0fc3a05cc00d62fc68556b77ad5a1dc/Library/Formula/imagemagick.rb >! /usr/local/Homebrew/Library/Taps/homebrew/homebrew-core/Formula/imagemagick.rb
$ brew install imagemagick
libv8
Ref: http://qiita.com/ooyabuh/items/32e7086917e29356b532
$ gem install libv8 -v '3.16.14.11' -- --with-system-v8
$ bundle config build.libv8 --with-system-v8
mysql2
Ref: http://nekonenene.hatenablog.com/entry/2016/10/31/061350
bundle config build.mysql2 --with-opt-lib=/usr/local/opt/openssl/lib --with-opt-include=-I/usr/local/opt/openssl/include
eventmachine
Ref: http://qiita.com/nownabe/items/c62574b63fd55ee31ed6
bundle config build.eventmachine --with-cppflags=-I/usr/local/opt/openssl/include