Installing therubyracer on Mac OS X 10.8 (Mountain Lion)

This worked for me on 2014-02-20 after MUCH searching!

1. brew tap homebrew/dupes
2. brew install apple-gcc42
3. export CC=/usr/local/Cellar/apple-gcc42/4.2.1-5666.3/bin/gcc-4.2
4. export CXX=/usr/local/Cellar/apple-gcc42/4.2.1-5666.3/bin/g++-4.2
5. export CPP=/usr/local/Cellar/apple-gcc42/4.2.1-5666.3/bin/cpp-4.2
6. sudo mv /usr/bin/g++ /usr/bin/g++_apple
7. sudo ln -sf /usr/local/Cellar/apple-gcc42/4.2.1-5666.3/bin/g++-4.2 /usr/bin/g++
8. gem uninstall libv8
9. gem install therubyracer -v=0.11.4
10. sudo mv /usr/bin/g++_apple /usr/bin/g++

See also http://stackoverflow.com/a/21453272/120818