[Simon: this should fix that -funfolding-use-threshold0 lint bug]

[Kevin: have a look at WwLib.mkWwBodies.  Isn't it a thing of beauty?
	Could you think about whether the CPR stuff could be cleaned
	up a bit?  The strictness stuff is much shorter.]


This commit tidies up WwLib.mkWwBodies, fixing a couple of bugs.

* One bug showed up when CPR made a worker return an unboxed tuple,
  but the worker didn't have any other arguments.  The "add a void arg"
  hack needed to be generalised a bit.

* The other bug showed up when booting the compiler.  There's a long
  comment near splitProductType in WwLib.lhs that explains the problem.