Use -threaded for iserv-proxy (#2385)

* Use `-threaded` for iserv-proxy

Fixes #2361

@luite tracked the failure down:

> It's an async IO call that fails, async and fdwait have some limitations on Windows. the threaded runtime doesn't use them

* Disable threaded for aarch64 cross GHC 9.6.7

Author: hamishmack

flake.lock

@@ -1053,6 +1053,14 @@ final: prev: {
                     setupBuildFlags = final.lib.mkForce [];
                   };
                 }];
+              } // final.lib.optionalAttrs (
+                     final.stdenv.hostPlatform.isAarch64
+                  && builtins.compareVersions final.buildPackages.haskell-nix.compiler.${compiler-nix-name}.version "9.8" < 0) {
+                # The th-dlls test fails for aarch64 cross GHC 9.6.7 when the threaded rts is used
+                cabalProjectLocal = ''
+                  package iserv-proxy
+                    flags: -threaded
+                '';
               } // final.lib.optionalAttrs (__compareVersions final.buildPackages.haskell-nix.compiler.${compiler-nix-name}.version "9.10" > 0) {
                   cabalProjectLocal = ''
                     allow-newer: *:base, *:bytestring