Add a missing check for -fcpr-off

Test Plan: validate

Reviewers: austin, bgamari, simonpj

Reviewed By: simonpj

Subscribers: simonpj, thomie

Differential Revision: https://phabricator.haskell.org/D1104

GHC Trac Issues: #10696

compiler/basicTypes/Demand.hs

@@ -1162,8 +1162,8 @@ nopDmdType = DmdType emptyDmdEnv [] topRes
 botDmdType = DmdType emptyDmdEnv [] botRes
 
 cprProdDmdType :: Arity -> DmdType
-cprProdDmdType _arity
-  = DmdType emptyDmdEnv [] (Dunno RetProd)
+cprProdDmdType arity
+  = DmdType emptyDmdEnv [] (vanillaCprProdRes arity)
 
 isNopDmdType :: DmdType -> Bool
 isNopDmdType (DmdType env [] res)