[ffigen] Disable enum warning for ObjC

[liamappelbe]

This warning is only relevant on Windows, so we don't need it for ObjC, which is only supported on iOS/macOS.

Fixes #1817

[github-actions]

PR Health

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
ffigen	Breaking	16.0.0	17.0.0-wip	17.0.0	✔️

API leaks ⚠️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package

Leaked API symbols

ffigen

Type AstNode Visitation Visitor BindingType NoLookUpBinding Binding Writer SymbolAddressWriter EnumClass EnumConstant UniqueNamer ObjCBuiltInFunctions ObjCImport Parameter ObjCMsgSendFunc ObjCMsgSendVariant ObjCMsgSendVariantFunc FunctionType ObjCInternalGlobal ObjCBlock ObjCListenerBlockTrampoline Func LookUpBinding LibraryImport BindingString BindingStringType ObjCInterface ObjCMethod ObjCProperty ObjCMethodKind ObjCMethodOwnership ObjCMethodFamily ObjCProtocol ObjCCategory Struct Compound CompoundMember CompoundType Union MacroConstant Constant UnnamedEnumConstant Global Typealias PointerType ImportedType ConfigSpec ConfigValue

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License Headers ✔️

// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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Files
pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/native_assets_builder/test_data/native_dynamic_linking/bin/native_dynamic_linking.dart
pkgs/objective_c/lib/src/ns_input_stream.dart