Turn libraryDynDirSupported back on.

Signed-off-by: Edward Z. Yang <[email protected]>

Author: ezyang

Cabal/Distribution/Simple/Compiler.hs

@@ -330,17 +330,13 @@ backpackSupported = ghcSupported "Support Backpack"
 libraryDynDirSupported :: Compiler -> Bool
 libraryDynDirSupported comp = case compilerFlavor comp of
   GHC ->
-    -- GHC patch still hasn't landed yet. When it does, update
-    -- this date and uncomment
-    {-
-      -- Not just v >= mkVersion [8,0,1,20161021], as there
+      -- Not just v >= mkVersion [8,0,1,20161022], as there
       -- are many GHC 8.1 nightlies which don't support this.
-    ((v >= mkVersion [8,0,1,20161021] && v < mkVersion [8,1]) ||
+    ((v >= mkVersion [8,0,1,20161022] && v < mkVersion [8,1]) ||
       v >= mkVersion [8,1,20161021])
-      -} False
   _   -> False
  where
-  _v = compilerVersion comp
+  v = compilerVersion comp
 
 -- | Does this compiler support Haskell program coverage?
 coverageSupported :: Compiler -> Bool