In ':show imports' take account of -XNoImplicitPrelude

Fixes Trac #8640

ghc/InteractiveUI.hs

@@ -2229,6 +2229,7 @@ showImports = do
 
       prel_imp
         | any isPreludeImport (rem_ctx ++ trans_ctx) = []
+        | not (xopt Opt_ImplicitPrelude dflags)      = []
         | otherwise = ["import Prelude -- implicit"]
 
       trans_comment s = s ++ " -- added automatically"