Fixed modulo by a power of 2 on A64.

Actually setting flags before checking them might be a good idea... :-/

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/200113003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19924 ce2b1a6d-e550-0410-aec6-3dcde31c8c00