Merged r15334 into 3.18 branch.

ia32: Restore missing temp register for LNumberTagU

BUG=v8:2692
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/19791003

git-svn-id: https://v8.googlecode.com/svn/branches/3.18@15836 ce2b1a6d-e550-0410-aec6-3dcde31c8c00