[turbofan] Improve code generation for inline comparisons with zero.

TEST=cctest,unittests
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/669133004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24832 ce2b1a6d-e550-0410-aec6-3dcde31c8c00