Explicit export lists for Main

Lack of explicit export list can degrade performance. The Main module in particular should always have an explicit export list that contains just the main function.

cabal-install/src/Distribution/Client/Init/Defaults.hs

@@ -165,15 +165,15 @@ myLibHs =
 
 myExeHs :: [String]
 myExeHs =
-  [ "module Main where"
+  [ "module Main (main) where"
   , ""
   , "main :: IO ()"
   , "main = putStrLn \"Hello, Haskell!\""
   ]
 
 myLibExeHs :: [String]
 myLibExeHs =
-  [ "module Main where"
+  [ "module Main (main) where"
   , ""
   , "import qualified MyLib (someFunc)"
   , ""