Uses a shorter opcode for movl and movb with immediates.
Make movl preferable to movq in Set(register, int64_t) and use Set in more places.

Review URL: http://codereview.chromium.org/6824074

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@7589 ce2b1a6d-e550-0410-aec6-3dcde31c8c00