M5 grade-2 tools: fix GCC 12 stringop-overflow guards

GCC 12 hardened -Wstringop-overflow detection emits -Werror on
tools/libnetgraph/msg.c:240 (strncpy 512 bytes into 32-byte
sg_data) and tools/ngctl/write.c:115 (strlcpy 254 bytes into
32-byte sg_data). Both files already had #pragma GCC diagnostic
push/pop blocks but guarded under "#if __GNUC__ >= 13", missing
GCC 12. Lower the guard to "#if __GNUC__ >= 12".

Net effect:
  - tools/sbin/{ifconfig, route, ipfw, arp, ndp, ngctl,
    netstat} all link cleanly (24-25M each)
  - tools/{libnetgraph, libutil, libmemstat, libxo, sysctl,
    top, traffic, knictl, compat} 9 verify-only PASS
  - libffcompat.a: 22 .o / 301K

Author: jfb8856606

tools/libnetgraph/msg.c

@@ -233,12 +233,12 @@ NgDeliverMsg(int cs, const char *path,
 	/* Prepare socket address */
 	sg->sg_family = AF_NETGRAPH;
 	/* XXX handle overflow */
-#if __GNUC__ >= 13
+#if __GNUC__ >= 12
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wstringop-overflow"
 #endif
 	strncpy(sg->sg_data, path, NG_PATHSIZ);
-#if __GNUC__ >= 13
+#if __GNUC__ >= 12
 #pragma GCC diagnostic pop
 #endif
 	sg->sg_len = strlen(sg->sg_data) + 1 + NGSA_OVERHEAD;

tools/ngctl/write.c

@@ -108,12 +108,12 @@ WriteCmd(int ac, char **av)
 	/* Send data */
 	sag->sg_len = 3 + strlen(hook);
 	sag->sg_family = AF_NETGRAPH;
-#if __GNUC__ >= 13
+#if __GNUC__ >= 12
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Wstringop-overflow"
 #endif
 	strlcpy(sag->sg_data, hook, sizeof(sagbuf) - 2);
-#if __GNUC__ >= 13
+#if __GNUC__ >= 12
 #pragma GCC diagnostic pop
 #endif
 	if (sendto(dsock, buf, len,