If you have macports on your path this is the likely cause of this issue.
you need to update your path so it uses the libtool from
/usr/bin and not the one on
export PATH=/usr/bin:$PATH $ sudo gem install libv8 -v '126.96.36.199' Building native extensions. This could take a while... Successfully installed libv8-188.8.131.52 1 gem installed