Fix typed lowering of JSAdd on non-number inputs.

R=rossberg@chromium.org
TEST=mjsunit/regress/regress-3476

Review URL: https://codereview.chromium.org/564823003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23883 ce2b1a6d-e550-0410-aec6-3dcde31c8c00