D50217.id154991.diff
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	diff --git a/sys/sys/cdefs.h b/sys/sys/cdefs.h
	--- a/sys/sys/cdefs.h
	+++ b/sys/sys/cdefs.h
	@@ -258,7 +258,8 @@
	* clang and gcc have different semantics for __warn_unused_result__: the latter
	* does not permit the use of a void cast to suppress the warning. Use
	* __result_use_or_ignore_check in places where a void cast is acceptable.
	- * This can be implemented by [[nodiscard]] from C23.
	+ *
	+ * This macro is deprecated; use __nodiscard in new code.
	*/
	#define __result_use_or_ignore_check __result_use_check
	#else
	@@ -295,6 +296,33 @@
	#define __noexcept_if(__c)
	#endif

	+/*
	+ * nodiscard attribute added in C++17 and C23, but supported by both LLVM and
	+ * GCC in earlier language versions, so we use __has_c{,pp}_attribute to test
	+ * for it.
	+ *
	+ * __nodiscard may be used on a function:
	+ * __nodiscard int f();
	+ *
	+ * or on a struct, union or enum:
	+ * struct __nodiscard S{};
	+ * struct S f();
	+ *
	+ * or in C++, on an object constructor.
	+ */
	+
	+#if defined(__cplusplus) && defined(__has_cpp_attribute)
	+#if __has_cpp_attribute(nodiscard)
	+#define __nodiscard [[nodiscard]]
	+#endif
	+#elif defined(__STDC_VERSION__) && defined(__has_c_attribute)
	+#if __has_c_attribute(__nodiscard__)
	+#define __nodiscard [[__nodiscard__]]
	+#endif
	+#else
	+#define __nodiscard
	+#endif
	+
	/*
	* We use `__restrict' as a way to define the `restrict' type qualifier
	* without disturbing older software that is unaware of C99 keywords.