Prepends the hsenv arguments instead of appending them.

yesod/GhcBuild.hs

@@ -54,7 +54,7 @@ import           Util               (consIORef, looksLikeModuleName)
 getBuildFlags :: IO [Located String]
 getBuildFlags = do
   argv0 <- fmap read $ readFile "yesod-devel/ghcargs.txt" -- generated by yesod-ghc-wrapper
-  argv0' <- addHsenvArgs argv0
+  argv0' <- prependHsenvArgv argv0
   let (minusB_args, argv1) = partition ("-B" `isPrefixOf`) argv0'
       mbMinusB | null minusB_args = Nothing
                | otherwise = Just (drop 2 (last minusB_args))
@@ -63,12 +63,12 @@ getBuildFlags = do
   (argv2, staticFlagWarnings) <- GHC.parseStaticFlags argv1'
   return argv2
 
-addHsenvArgs :: [String] -> IO [String]
-addHsenvArgs argv = do
+prependHsenvArgv :: [String] -> IO [String]
+prependHsenvArgv argv = do
   env <- getEnvironment
   return $ case (lookup "HSENV" env) of
              Nothing -> argv
-             _       -> argv ++ hsenvArgv
+             _       -> hsenvArgv ++ argv
                  where hsenvArgv = words $ fromMaybe "" (lookup "PACKAGE_DB_FOR_GHC" env)
 
 buildPackage :: [Located String] -> FilePath -> FilePath -> IO Bool