+Note [Stupid theta]
+~~~~~~~~~~~~~~~~~~~
+Trac #3850 complains about a regression wrt 6.10 for
+ data Show a => T a
+There is no reason not to allow the stupid theta if there are no data
+constructors. It's still stupid, but does no harm, and I don't want
+to cause programs to break unnecessarily (notably HList). So if there
+are no data constructors we allow h98_style = True
+