Windows only: delay adding targetDir dependencies

* hptool/src/OS/Win.hs
  * Move the enumeration of the targetDir contents until
    after we are actually complete with this directory.  This
    step needs to be timed differently than the other builds
    since on the Windows builds, HP and GHC are installed
    into a single directory.  Without this, Shake will
    complain that the directory contents of targetDir have
    changed (upon populating targetDir with the HP-specific
    packages) since the time of making a dependency on them
    (which would happen after GHC is placed in targetDir).

Author: randen

hptool/src/OS/Win.hs

@@ -96,10 +96,7 @@ winOsFromConfig BuildConfig{..} = os
     whenM :: (Monad m) => m Bool -> m () -> m ()
     whenM mp m = mp >>= \p -> when p m
 
-    osTargetAction = do
-        -- Now, targetDir is actually ready to snapshot (we skipped doing
-        -- this in osGhcTargetInstall).
-        void $ getDirectoryFiles "" [targetDir ++ "//*"]
+    osTargetAction = return ()
 
     osGhcDbDir = winGhcPackageDbDir
 
@@ -138,10 +135,15 @@ winOsFromConfig BuildConfig{..} = os
 
         osProduct %> \_ -> do
             need $ [dir ghcLocalDir, phonyTargetDir, vdir ghcVirtualTarget]
-                   ++ winNeeds
 
             copyWinTargetExtras bc
 
+            -- Now, targetDir is actually ready to snapshot (we skipped doing
+            -- this in osGhcTargetInstall).
+            void $ getDirectoryFiles "" [targetDir ++ "//*"]
+
+            need winNeeds
+
             -- Now, it is time to make sure there are no problems with the
             -- conf files copied to
             localCommand' [] "ghc-pkg"