Revert "Fix windows validate."

This reverts commit ef37580d.

Now that commit e2330b6d has been reverted
this change is now needed.

compiler/main/DynFlags.hs

@@ -220,6 +220,7 @@ import System.Console.Terminfo (SetupTermError, Terminal, getCapability,
                                 setupTermFromEnv, termColors)
 import System.Posix (queryTerminal, stdError)
 #elif defined mingw32_HOST_OS
+import Foreign (Ptr, with, peek)
 import System.Environment (lookupEnv)
 import qualified Graphics.Win32 as Win32
 #endif