Introduce PushQuad and PopQuad for x64 port.

R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/238253013

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21080 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Handlification TODOs in scanner and string stream resolved.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/251263004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21081 ce2b1a6d-e550-0410-aec6-3dcde31c8c00