Revert "compiler: Disable atomic renaming on Windows"

The original reason this was disabled should be fixed by the previous
commit.

This reverts commit 1c1b63d6.

compiler/utils/Util.hs

@@ -1291,8 +1291,7 @@ modificationTimeIfExists f = do
 -- also results in a skip.
 
 withAtomicRename :: (MonadIO m) => FilePath -> (FilePath -> m a) -> m a
-withAtomicRename targetFile f
-  | enableAtomicRename = do
+withAtomicRename targetFile f = do
   -- The temp file must be on the same file system (mount) as the target file
   -- to result in an atomic move on most platforms.
   -- The standard way to ensure that is to place it into the same directory.
@@ -1303,17 +1302,6 @@ withAtomicRename targetFile f
   liftIO $ renameFile temp targetFile
   return res
 
-  | otherwise = f targetFile
-  where
-    -- As described in #16450, enabling this causes spurious build failures due
-    -- to apparently missing files.
-    enableAtomicRename :: Bool
-#if defined(mingw32_BUILD_OS)
-    enableAtomicRename = False
-#else
-    enableAtomicRename = True
-#endif
-
 -- --------------------------------------------------------------
 -- split a string at the last character where 'pred' is True,
 -- returning a pair of strings. The first component holds the string