haskellPackages: allow local networking when using iserv-proxy (#497113)

pkgs/development/haskell-modules/generic-builder.nix

@@ -261,6 +261,8 @@ in
   __onlyPropagateKnownPkgConfigModules ? false,
   enableExternalInterpreter ?
     isCross && crossSupport.canProxyTH && crossSupport.needsExternalInterpreterSetup,
+  # iserv-proxy needs local network access
+  __darwinAllowLocalNetworking ? stdenv.hostPlatform.isDarwin && enableExternalInterpreter,
 }@args:
 
 assert editedCabalFile != null -> revision != null;
@@ -1138,5 +1140,8 @@ lib.fix (
     // optionalAttrs (disallowedRequisites != [ ] || disallowGhcReference) {
       disallowedRequisites = disallowedRequisites ++ (if disallowGhcReference then [ ghc ] else [ ]);
     }
+    // optionalAttrs (__darwinAllowLocalNetworking || args ? __darwinLocalNetworking) {
+      __darwinAllowLocalNetworking = true;
+    }
   )
 )