fix windows build (and make --stop work on windows, incidentially)

The Utility.PID will clean up other code soon.

Utility/PID.hs

@@ -0,0 +1,31 @@
+{- process ids
+ -
+ - Copyright 2014 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+{-# LANGUAGE CPP #-}
+
+module Utility.PID where
+
+#ifndef mingw32_HOST_OS
+import System.Posix.Types (ProcessID)
+import System.Posix.Process (getProcessID)
+#else
+import System.Win32.Process (ProcessId)
+import System.Win32.Process.Current (getCurrentProcessId)
+#endif
+
+#ifndef mingw32_HOST_OS
+type PID = ProcessID
+#else
+type PID = ProcessId
+#endif
+
+getPID :: IO PID
+#ifndef mingw32_HOST_OS
+getPID = getProcessID
+#else
+getPID = getCurrentProcessId
+#endif