I would appreciate some help in getting gem install therubyracer to work. Here is the error:
$ gem install therubyracer
Building native extensio
I got a similar issue, but it was also complaining about not finding g++-4.2. I did have XCode command line tools installed, but it was looking for /usr/bin/g++-4.2, I had g++ (which was a symbolic link pointing to llvm-g++-4.2). Anyway, I just created a symbolic link to g++ and tried the bundle install again... it worked!
$ cd /usr/bin
$ sudo ln -s g++ g++-4.2