Correct the type of interpWays

ghc-api-compat.cabal

@@ -121,6 +121,8 @@ library
    if impl(ghc >= 9.0)
       hs-source-dirs:   src
       exposed-modules:  Outputable DynFlags
+      build-depends: 
+         containers >= 0.6.0 && <= 0.6.5
       reexported-modules:
            GHC.Rename.Bind                as RnBinds
          , GHC.Rename.Env                 as RnEnv

src/DynFlags.hs

@@ -12,7 +12,7 @@ module DynFlags
   )
 where
 
-import Data.Foldable (toList)
+import Data.Set (Set)
 import GHC.Driver.Session
 #if MIN_VERSION_GLASGOW_HASKELL(9,2,0,0)
 import GHC.Platform.Ways
@@ -26,6 +26,5 @@ buildTag = waysBuildTag . ways
 dynamicGhc :: Bool
 dynamicGhc = hostIsDynamic
 
-interpWays :: [Way]
-interpWays = toList hostFullWays
-
+interpWays :: Set Way
+interpWays = hostFullWays