Add Terminate operator.

Terminate is need for non-terminating loops (NTLs) that can appear after optimizing control flow. It gathers the control and effect(s) from a NTL and connects them to end so that they are not dead-code removed.

R=mstarzinger@chromium.org
BUG=

Review URL: https://codereview.chromium.org/651843004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24812 ce2b1a6d-e550-0410-aec6-3dcde31c8c00