[lld] [llvm] [libcxx] [flang] [clang] [libc++][streams] P1759R6: Native handles and file streams (PR #76632)

[Mark de Wever via cfe-commits]

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@@ -0,0 +1,81 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_STD_INPUT_OUTPUT_FILE_STREAMS_FSTREAMS_TEST_HELPERS_H
+#define TEST_STD_INPUT_OUTPUT_FILE_STREAMS_FSTREAMS_TEST_HELPERS_H
+
+#if _LIBCPP_STD_VER >= 26
+
+#  include <cassert>
+#  include <concepts>
+#  include <cstdio>
+#  include <fstream>
+#  include <filesystem>
+#  include <type_traits>
+#  include <utility>
+
+#  if defined(_LIBCPP_WIN32API)
+#    define WIN32_LEAN_AND_MEAN
+#    define NOMINMAX
+#    include <io.h>
+#    include <windows.h>
+#  else
+#    include <fcntl.h>
+#  endif
+
+#  include "platform_support.h"
+
+#  if defined(_LIBCPP_WIN32API)
+using HandleT = void*; // HANDLE
+
+bool is_handle_valid(void* handle) {
----------------
mordante wrote:

```suggestion
inline bool is_handle_valid(void* handle) {
```
The same for the other functions in the header.

https://github.com/llvm/llvm-project/pull/76632