Avoid a smi check when comparing an unknown to a constant smi for equality on ia32 and x64 platforms.
Review URL: http://codereview.chromium.org/2897013

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5077 ce2b1a6d-e550-0410-aec6-3dcde31c8c00