deps: cherry-pick 2e4da65 from v8's 4.8 upstream

deps: cherry-pick 2e4da65 from v8's 4.8 upstream

Float v8 patch, which has been committed to v8 master and
backported to 4.8 and 4.9 in google repos, onto 4.8 v8 in
deps to resolve https://github.com/nodejs/node/issues/5089

Original title/commit from google repos for 4.8 is:
 PPC: [turbofan] Support for CPU models lacking isel.
 https://github.com/v8/v8/commit/2e4da65332753a4fed679be81634b7685616b1fd

PR-URL: https://github.com/nodejs/node/pull/5293
Fixes: https://github.com/nodejs/node/issues/5089
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: jbergstroem - Johan Bergström <bugs@bergstroem.nu>