Use stable-haskell/iserv-proxy?ref=iserv-syms for ghc <9.4

Author: hamishmack

overlays/ghc-packages.nix

@@ -75,18 +75,10 @@ let
       libiserv     = "libraries/libiserv";
     } // final.lib.optionalAttrs (!final.stdenv.hostPlatform.isGhcjs || builtins.compareVersions ghcVersion "9" > 0) {
       ghc          = "compiler";
-    } // (
-      if builtins.compareVersions ghcVersion "9.4" < 0
-        then {
-          # As of GHC 9.4 this has been split out of the GHC repo and
-          # is now in the iserv-proxy flake input
-          iserv-proxy  = "utils/iserv-proxy";
-        }
-        else {
-          genprimopcode = "utils/genprimopcode";
-          deriveConstants = "utils/deriveConstants";
-        }
-    ) // final.lib.optionalAttrs (!final.stdenv.hostPlatform.isGhcjs || builtins.compareVersions ghcVersion "8.10.5" >= 0) {
+    } // final.lib.optionalAttrs (builtins.compareVersions ghcVersion "9.4" >= 0) {
+      genprimopcode = "utils/genprimopcode";
+      deriveConstants = "utils/deriveConstants";
+    } // final.lib.optionalAttrs (!final.stdenv.hostPlatform.isGhcjs || builtins.compareVersions ghcVersion "8.10.5" >= 0) {
       # Not sure why, but this is missing from older ghcjs versions
       remote-iserv = "utils/remote-iserv";
     } // final.lib.optionalAttrs (builtins.compareVersions ghcVersion "9.0.1" >= 0) {

overlays/haskell.nix

@@ -1035,14 +1035,6 @@ final: prev: {
         withInputs = final.recurseIntoAttrs;
 
         iserv-proxy-exes = __mapAttrs (compiler-nix-name: _ghc:
-          if __compareVersions final.buildPackages.haskell-nix.compiler.${compiler-nix-name}.version "9.4" <0
-            then {
-              inherit (final.buildPackages.ghc-extra-packages.${compiler-nix-name}.iserv-proxy.components.exes) iserv-proxy;
-              # remote-iserv however needs to come from the regular packages as it has to
-              # run on the target host.
-              iserv-proxy-interpreter = final.ghc-extra-packages.${compiler-nix-name}.remote-iserv.components.exes.remote-iserv;
-            }
-          else
             let
               exes = pkgs: (pkgs.haskell-nix.cabalProject' ({pkgs, ...}: {
                 name = "iserv-proxy";