Merged r17130 into trunk branch.

Only crosscompile binary op stubs if we compile a snapshot.

R=verwaest@chromium.org
BUG=

Review URL: https://codereview.chromium.org/26279012

git-svn-id: https://v8.googlecode.com/svn/trunk@17132 ce2b1a6d-e550-0410-aec6-3dcde31c8c00