Don't instantaite when typechecking a pattern synonym
Don't instantaite when typechecking a pattern synonym

Fixes most of the cases in Trac #12762

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