Use 'equalFilePath' instead of '/='.

cabal-install/Distribution/Client/Install.hs

@@ -50,7 +50,7 @@ import System.Directory
          ( getTemporaryDirectory, doesDirectoryExist, doesFileExist,
            createDirectoryIfMissing, removeFile, renameDirectory )
 import System.FilePath
-         ( (</>), (<.>), takeDirectory )
+         ( (</>), (<.>), equalFilePath, takeDirectory )
 import System.IO
          ( openFile, IOMode(AppendMode), hClose )
 import System.IO.Error
@@ -1191,7 +1191,8 @@ installLocalTarballPackage verbosity jobLimit pkgid
           distDirPathTmp = absUnpackedPath </> (defaultDistPref ++ "-tmp")
           distDirPathNew = absUnpackedPath </> distPref
       distDirExists <- doesDirectoryExist distDirPath
-      when (distDirExists && distDirPath /= distDirPathNew) $ do
+      when (distDirExists
+            && (not $ distDirPath `equalFilePath` distDirPathNew)) $ do
         -- NB: we need to handle the case when 'distDirPathNew' is a
         -- subdirectory of 'distDirPath' (e.g. the former is
         -- 'dist/dist-sandbox-3688fbc2' and the latter is 'dist').