GHC builds recursive coerctions when using recursive type families

Consider

{-# LANGUAGE TypeFamilies, GADTs, UndecidableInstances #-}
type family F a
type instance F () = F ()
data A where
  A :: F () ~ () => A
x :: A
x = A
main = seq A (return ())

On GHC 7.6.3 it yields a context reduction stack overflow (despite F () ~ () being put into the “solved funeqs” list).

In HEAD, a recursive dictionary is built, but then detected:

[1 of 1] Compiling Foo              ( Foo.hs, Foo.o )
        ghc-stage2: panic! (the 'impossible' happened)
          (GHC version 7.7.20131108 for x86_64-unknown-linux):
        	Cycle in coercion bindings
            [[cobox_ayX{v} [lid]
                = CO main:Foo.TFCo:R:F(){tc rob}[0] ; cobox_ayZ{v} [lid],
              cobox_ayZ{v} [lid] = CO cobox_ayX{v} [lid] ; cobox_az0{v} [lid]]]
        
        Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Either this panic needs to be turned into an error, or we need to prevent recursive dictionaries for when solving funeqs (similar to how we do it for Coercible).