This is a fairly complete implementation, however
two 'panic's have been placed in the critical path
where the implementation is still a bit lacking so
do not expect it to run quite yet.

One call to panic is because we still need to create
a GC block for procedures that don't have them yet.
(cmm/CmmCPS.hs:continuationToProc)

The other is due to the need to convert from a
ContinuationInfo to a CmmInfo.
(codeGen/CgInfoTbls.hs:emitClosureCodeAndInfoTable)
(codeGen/CgInfoTbls.hs:emitReturnTarget)