Fix the test with -O
Fix the test with -O

Static string optimisation means we get a ForeignPtr with an IORef
inside it, leading to a different error.

sdiehl/ghc,ezyang/ghc,shlevy/ghc,olsner/ghc,sdiehl/ghc,shlevy/ghc,sdiehl/ghc,ezyang/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,olsner/ghc,olsner/ghc,ezyang/ghc,ezyang/ghc,sdiehl/ghc,olsner/ghc,shlevy/ghc,olsner/ghc,sdiehl/ghc,olsner/ghc,olsner/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,ezyang/ghc,shlevy/ghc,shlevy/ghc