gem uninstall libv8
brew install v8
gem install therubyracer
gem install libv8 -v '3.16.14.3' -- --with-system-v8
this is the only way it worked for me on 10.10 (ruby 2.1.2)
Or try gem install libv8 -v 'XX.XX.XX' -- --with-system-v8
adding the version of the gem 🙂
UPDATE for Mac OS Catalina:
brew tap homebrew/versions
brew install v8@3.15
brew link --force v8@3.15
gem install libv8 -v 'XX.XX.XX' -- --with-system-v8
gem install therubyracer