Implement foldr/cons/build

There seem to be various issues with general fold/cons and even cons/build rules, but it seems pretty clear to me that the simple fold/cons/build rule is a good idea. It doesn't do much for nofib allocation, but it seems to improve some other analyses and speed several benchmarks up, including speeding up some things that other fusion changes slowed down. I say "seems to" because I never trust my timings much at all.

{-# RULES
"foldr/cons/build" forall c n x (g::forall b. (a->b->b) -> b -> b) .
                           foldr c n (x:build g) = c x (g c n)
 #-}

Trac metadata

Trac field	Value
Version	7.9
Type	Task
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
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CC	ekmett, hvr
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