https://trac.macports.org/ticket/66092

--- a/include/tradstdc.h.orig	2022-12-27 17:46:35
+++ b/include/tradstdc.h	2022-12-27 17:48:14
@@ -431,8 +431,11 @@
 #define NORETURN __attribute__((noreturn))
 /* disable gcc's __attribute__((__warn_unused_result__)) since explicitly
    discarding the result by casting to (void) is not accepted as a 'use' */
+#ifndef __clang__
 #define __warn_unused_result__ /*empty*/
 #define warn_unused_result /*empty*/
+#endif
+
 #endif
 #endif