topgrade: fix Darwin build (#541141)

pkgs/by-name/to/topgrade/package.nix

@@ -4,6 +4,7 @@
   fetchFromGitHub,
   rustPlatform,
   installShellFiles,
+  llvmPackages,
 }:
 
 rustPlatform.buildRustPackage (finalAttrs: {
@@ -21,14 +22,18 @@ rustPlatform.buildRustPackage (finalAttrs: {
 
   nativeBuildInputs = [
     installShellFiles
-  ];
+  ]
+  # TODO: Remove once #536365 reaches this branch
+  ++ lib.optionals stdenv.hostPlatform.isDarwin [ llvmPackages.lld ];
 
-  env.NIX_CFLAGS_COMPILE = toString (
-    lib.optionals stdenv.hostPlatform.isDarwin [
+  env = lib.optionalAttrs stdenv.hostPlatform.isDarwin {
+    NIX_CFLAGS_COMPILE = toString [
       "-framework"
       "AppKit"
-    ]
-  );
+    ];
+    # TODO: Remove once #536365 reaches this branch
+    NIX_CFLAGS_LINK = "-fuse-ld=lld";
+  };
 
   postInstall = lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
     installShellCompletion --cmd topgrade \