X64: Added dummy definitions of needed functions.

All functions added in assembler-x64.cc. They should be distributed to where they belong when they are implemented.

Review URL: http://codereview.chromium.org/113334


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1933 ce2b1a6d-e550-0410-aec6-3dcde31c8c00