POSIX.1-2024 standardizes and requires SIGWINCH.

Index: signal.h
===================================================================
RCS file: /cvs/src/sys/sys/signal.h,v
diff -u -p -r1.29 signal.h
--- signal.h	18 Apr 2018 16:05:20 -0000	1.29
+++ signal.h	22 Feb 2026 18:27:31 -0000
@@ -80,8 +80,10 @@
  #define	SIGXFSZ	25	/* exceeded file size limit */
  #define	SIGVTALRM 26	/* virtual time alarm */
  #define	SIGPROF	27	/* profiling time alarm */
-#if __BSD_VISIBLE
+#if __BSD_VISIBLE || __POSIX_VISIBLE >= 202405
  #define SIGWINCH 28	/* window size changes */
+#endif
+#if __BSD_VISIBLE
  #define SIGINFO	29	/* information request */
  #endif
  #define SIGUSR1 30	/* user defined signal 1 */