Fix warning about signed comparison and drop WARNS for ktrdump(8).

Reviewed By:		jhb, imp
Differential Revision:	https://reviews.freebsd.org/D29381

(cherry picked from commit 9e5aeba51b)

usr.bin/ktrdump/Makefile

@@ -4,6 +4,4 @@ PROG=	ktrdump
 LIBADD=	kvm
 MAN=	ktrdump.8
 
-WARNS?=	2
-
 .include <bsd.prog.mk>

usr.bin/ktrdump/ktrdump.c

@@ -56,11 +56,11 @@ __FBSDID("$FreeBSD$");
 static void usage(void);
 
 static struct nlist nl[] = {
-	{ "_ktr_version" },
-	{ "_ktr_entries" },
-	{ "_ktr_idx" },
-	{ "_ktr_buf" },
-	{ NULL }
+	{ .n_name = "_ktr_version" },
+	{ .n_name = "_ktr_entries" },
+	{ .n_name = "_ktr_idx" },
+	{ .n_name = "_ktr_buf" },
+	{ .n_name = NULL }
 };
 
 static int cflag;
@@ -262,7 +262,7 @@ main(int ac, char **av)
 		fprintf(out, "\n");
 	}
 
-	tlast = -1;
+	tlast = UINTPTR_MAX;
 	/*
 	 * Now tear through the trace buffer.
 	 *
@@ -327,7 +327,7 @@ next:			if ((c = *p++) == '\0')
 		if (tflag) {
 			tnow = (uintmax_t)buf[i].ktr_timestamp;
 			if (rflag) {
-				if (tlast == -1)
+				if (tlast == UINTPTR_MAX)
 					tlast = tnow;
 				fprintf(out, "%16ju ", !iflag ? tlast - tnow :
 				    tnow - tlast);