icu uses the same identifiers, so we can't just #undef them

BUG=v8:2745
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/18209003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15565 ce2b1a6d-e550-0410-aec6-3dcde31c8c00