FFI: Revisit fix pass small ints in foreign call wrappers

Since commit be5d74ca small ints/words are passed according to their
natural size which obsoletes fix from commit 01f7052c.

Reverted 01f7052c but kept the introduced test case.

compiler/GHC/HsToCore/Foreign/Decl.hs

@@ -541,36 +541,15 @@ mkFExportCBits dflags c_nm maybe_target arg_htys res_hty is_IO_res_ty cc
                 SDoc,           -- C type
                 Type,           -- Haskell type
                 CmmType)]       -- the CmmType
-  arg_info  = [ let stg_type = showStgType ty
-                    cmm_type = typeCmmType platform (getPrimTyOf ty)
-                    stack_type
-                      = if int_promote (typeTyCon ty)
-                        then text "HsWord"
-                        else stg_type
-                in
-                (arg_cname n stg_type stack_type,
+  arg_info  = [ let stg_type = showStgType ty in
+                (arg_cname n stg_type,
                  stg_type,
                  ty,
-                 cmm_type)
+                typeCmmType platform (getPrimTyOf ty))
               | (ty,n) <- zip arg_htys [1::Int ..] ]
 
-  int_promote ty_con
-    | ty_con `hasKey` int8TyConKey = True
-    | ty_con `hasKey` int16TyConKey = True
-    | ty_con `hasKey` int32TyConKey
-    , platformWordSizeInBytes platform > 4
-    = True
-    | ty_con `hasKey` word8TyConKey = True
-    | ty_con `hasKey` word16TyConKey = True
-    | ty_con `hasKey` word32TyConKey
-    , platformWordSizeInBytes platform > 4
-    = True
-    | otherwise = False
-
-
-  arg_cname n stg_ty stack_ty
-        | libffi    = parens (stg_ty) <> char '*' <>
-                      parens (stack_ty <> char '*') <>
+  arg_cname n stg_ty
+        | libffi    = char '*' <> parens (stg_ty <> char '*') <>
                       text "args" <> brackets (int (n-1))
         | otherwise = text ('a':show n)