As you can see below, libv8 installs fine, but therubyracer doesn\'t. I\'m using Mac 10.7.4.
~/.rvm/rubies/ruby-1.9.3-p125/lib/ruby/1.9.1> gem install lib
I had this same problem when I upgraded from OSX Mountain Lion to OSX Mavericks.
Upgrading from ruby-1.8.7-p354 to ruby-1.8.7-375 did the trick for me. If you are on ruby-1.93-p125, you may want to try upgrading to 1.9.3-rc1 (which is above p484 already)
libv8 (3.16.14.3-x86_64-darwin-13) and the therubyracer (0.12.0) gems installed without problem.
assuming you use rbenv:
rbenv install 1.9.3-rc1
rbenv rehash
rbenv shell 1.9.3-rc1
bundle install