fixup #if 0 stubs to use #ifndef mingw32_HOST_OS

That's needed in files used to build the configure program.
For the other files, I'm keeping my __WINDOWS__ define, as I find that much easier to type.
I may search and replace it to use the mingw32_HOST_OS thing later.

Command/Fsck.hs

@@ -30,7 +30,7 @@ import qualified Option
 import Types.Key
 import Utility.HumanTime
 
-#if 0
+#ifndef mingw32_HOST_OS
 import System.Posix.Process (getProcessID)
 #endif
 import Data.Time.Clock.POSIX