Pre-existing pkgs: add system-cxx-std-lib (#2382)

Author: amesgen

overlays/haskell.nix

@@ -1118,6 +1118,8 @@ final: prev: {
             "semaphore-compat"
             "stm"
             "xhtml"
+          ] ++ final.lib.optionals (builtins.compareVersions ghc.version "9.4" > 0) [
+            "system-cxx-std-lib"
           ] ++ final.lib.optionals (
                   !final.stdenv.targetPlatform.isGhcjs
                && !final.stdenv.targetPlatform.isWindows