Make build/gyp_v8 cope with ninja on linux

ninja doesn't support/need the output dir and generator dir flags

BUG=v8:3252
R=machenbach@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/222023004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20462 ce2b1a6d-e550-0410-aec6-3dcde31c8c00