Revert r23916, r23917 for breaking 64-bit tests.

"Use unsigned type bitsets to limit undefined behaviour".

TBR=rossberg@chromium.org

Review URL: https://codereview.chromium.org/563283003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23922 ce2b1a6d-e550-0410-aec6-3dcde31c8c00