Skip json2 on 64 bits debug.

BUG=3681
LOG=n
TBR=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/701353003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25186 ce2b1a6d-e550-0410-aec6-3dcde31c8c00