inputs are heap numbers or the result is a heap number (only with
SSE2).  Make it possible for a deferred code object to work without
spilling all registers.
Review URL: http://codereview.chromium.org/3054047

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5215 ce2b1a6d-e550-0410-aec6-3dcde31c8c00