Remove unimplemented instructions from x64 assembler.  Add operand-size
suffixes to add, sub, inc, dec, and cmp.
Review URL: http://codereview.chromium.org/118380

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2139 ce2b1a6d-e550-0410-aec6-3dcde31c8c00