Allocate a fresh META unique in newMetaKindVar

Fixes Trac #7176 on the branch.  HEAD has a better fix
(the big patch to untouchable handling)

compiler/typecheck/TcMType.lhs

@@ -113,7 +113,7 @@ import Data.List        ( (\\), partition, mapAccumL )
 
 \begin{code}
 newMetaKindVar :: TcM TcKind
-newMetaKindVar = do { uniq <- newUnique
+newMetaKindVar = do { uniq <- newMetaUnique
 		    ; ref <- newMutVar Flexi
 		    ; return (mkTyVarTy (mkMetaKindVar uniq ref)) }