Change tests status for x64, make test runner pass --arch flag to Scons, add to x64 disassembler.  Copied from http://codereview.chromium.org/155346 so it can be committed.
Review URL: http://codereview.chromium.org/149608

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2456 ce2b1a6d-e550-0410-aec6-3dcde31c8c00