Disable weak embedded objects in optimized code because of failing test.

BUG=test/mjsunit/json.js fails
R=bmeurer@chromium.org

Review URL: https://chromiumcodereview.appspot.com/25982002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17103 ce2b1a6d-e550-0410-aec6-3dcde31c8c00