I don\'t manage to install therubyracer gem on Yosemite 10.10.
Here is the log:
11:53 $ gem install libv8 -v \'3.16.14.3\' -- --with-system-v8 Building
What worked for me, based on the following comment,
https://github.com/cowboyd/therubyracer/issues/304#issuecomment-62046085
was to remove Gemfile.lock and then run bundle install