Fixed constant folding for Math.clz32.

LOG=y
BUG=347906
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/184353002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19609 ce2b1a6d-e550-0410-aec6-3dcde31c8c00