This fixes the following error:

mh_init.c:1142:17: error: 'TIOCGWINSZ' undeclared (first use in this function); did you mean 'LIOCGETS'?

--- mailutils-3.13/mh/mh_init.c.orig	2021-07-16 19:50:58.000000000 +0000
+++ mailutils-3.13/mh/mh_init.c	2021-12-05 16:03:58.165128225 +0000
@@ -30,6 +30,10 @@
 #include <fnmatch.h>
 #include <sys/ioctl.h>
 
+#ifdef	__sun
+#include <sys/termios.h>
+#endif
+
 void
 mh_init (void)
 {