Pass -Goutput_dir=. to the make generator.

This makes it possible to remove the builddir_name hack added in r238632.

BUG=315004

Patch from Nico Weber <thakis@chromium.org>.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/98753003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18257 ce2b1a6d-e550-0410-aec6-3dcde31c8c00