pgrep naively appends the delimiter to all PIDs including the last

e.g. "pgrep -d, getty" outputs "1399,1386,1309,1308,1307,1306,1305,1302,"
Ensure the list is correctly delimited by suppressing the emission of the
delimiter after the final PID.

Reviewed by:	imp, kib
MFC after:	1 week
Sponsored by:	Netflix, Inc.
Differential Revision:	https://reviews.freebsd.org/D8537

bin/pkill/pkill.c

@@ -43,6 +43,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/user.h>
 
 #include <assert.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <limits.h>
@@ -656,10 +657,12 @@ killact(const struct kinfo_proc *kp)
 static int
 grepact(const struct kinfo_proc *kp)
 {
+	static bool first = true;
 
-	show_process(kp);
-	if (!quiet)
+	if (!quiet && !first)
 		printf("%s", delim);
+	show_process(kp);
+	first = false;
 	return (1);
 }