imsg.h needs pid_t, so I think it still needs to include sys/types.h.
Found by sthen via audio/amused build failure.

Index: imsg.h
===================================================================
RCS file: /cvs/src/lib/libutil/imsg.h,v
diff -u -p -r1.23 imsg.h
--- imsg.h	4 Jun 2025 09:08:52 -0000	1.23
+++ imsg.h	5 Jun 2025 08:06:10 -0000
@@ -22,6 +22,7 @@
 #ifndef _IMSG_H_
 #define _IMSG_H_
 
+#include <sys/types.h>
 #include <sys/queue.h>
 #include <stddef.h>
 #include <stdint.h>