An untagged int32 has zeros in the upper half even if it is negative.
Using cmpq to compare such numbers will incorrectly ignore the sign.

BUG=164442
R=mvstanton@chromium.org

Review URL: https://chromiumcodereview.appspot.com/11665007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13273 ce2b1a6d-e550-0410-aec6-3dcde31c8c00