Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__functional/mem_fn.h

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+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP___FUNCTIONAL_MEM_FN_H
+#define _LIBCPP___FUNCTIONAL_MEM_FN_H
+
+#include <__config>
+#include <__functional/binary_function.h>
+#include <__functional/invoke.h>
+#include <__functional/weak_result_type.h>
+#include <__utility/forward.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp>
+class __mem_fn : public __weak_result_type<_Tp>
+{
+public:
+    // types
+    typedef _Tp type;
+private:
+    type __f_;
+
+public:
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
+    __mem_fn(type __f) _NOEXCEPT : __f_(__f) {}
+
+    // invoke
+    template <class... _ArgTypes>
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
+
+    typename __invoke_return<type, _ArgTypes...>::type
+    operator() (_ArgTypes&&... __args) const {
+        return std::__invoke(__f_, std::forward<_ArgTypes>(__args)...);
+    }
+};
+
+template<class _Rp, class _Tp>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
+__mem_fn<_Rp _Tp::*>
+mem_fn(_Rp _Tp::* __pm) _NOEXCEPT
+{
+    return __mem_fn<_Rp _Tp::*>(__pm);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FUNCTIONAL_MEM_FN_H