System.Posix.Terminal.PosixString: Fix imports in HAVE_OPENPTY path

This appears to have broken with the `os-string` split of
`filepath-1.5`.

System/Posix/Terminal/PosixString.hsc

@@ -72,12 +72,18 @@ module System.Posix.Terminal.PosixString (
 import Foreign
 import System.Posix.Types
 import System.Posix.Terminal.Common
+
 #ifndef HAVE_OPENPTY
-import qualified System.OsPath.Data.ByteString.Short as SBS
-import System.Posix.IO.ByteString (defaultFileFlags, openFd, noctty, OpenMode(ReadWrite))
 import Data.ByteString.Char8 as B ( pack, )
-import qualified System.OsPath.Data.ByteString.Short as BC
+import System.Posix.IO.ByteString (defaultFileFlags, openFd, noctty, OpenMode(ReadWrite))
 import System.OsString.Internal.Types (PosixString(..))
+#if MIN_VERSION_filepath(1,5,0)
+import qualified System.OsString.Data.ByteString.Short as SBS
+import qualified System.OsString.Data.ByteString.Short as BC
+#else
+import qualified System.OsPath.Data.ByteString.Short as SBS
+import qualified System.OsPath.Data.ByteString.Short as BC
+#endif
 #endif
 
 import Foreign.C hiding (

cabal.project.wasm32-wasi

@@ -1,6 +1,9 @@
 packages: .
 
 package unix
+  -- Necessary as otherwise the `allow-newer` below will cause cabal to fail to
+  -- infer a consistent value of this flag.
+  flags: +os-string
   ghc-options: -Wno-unused-imports
 
 write-ghc-environment-files: always