Add Float64Floor, Float64Ceil, Float64RoundTruncate, Float64RoundTiesAway operators.

These operators are not supported by any backends yet, and a backend is free to not support them.

R=bmeurer@chromium.org
TEST=unittest/machine-operator

Review URL: https://codereview.chromium.org/668173002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24874 ce2b1a6d-e550-0410-aec6-3dcde31c8c00