https://bugs.gentoo.org/437108

always accept the -4 option even if we don't have IPv6 support enabled.
the relay code does this already.

--- a/client/dhclient.c
+++ b/client/dhclient.c
@@ -170,8 +170,8 @@ main(int argc, char **argv) {
 		if (!strcmp(argv[i], "-r")) {
 			release_mode = 1;
 			no_daemon = 1;
-#ifdef DHCPv6
 		} else if (!strcmp(argv[i], "-4")) {
+#ifdef DHCPv6
 			if (local_family_set && local_family != AF_INET)
 				log_fatal("Client can only do v4 or v6, not "
 					  "both.");
--- a/server/dhcpd.c
+++ b/server/dhcpd.c
@@ -373,8 +373,8 @@ main(int argc, char **argv) {
 		} else if (!strcmp (argv [i], "-q")) {
 			quiet = 1;
 			quiet_interface_discovery = 1;
-#ifdef DHCPv6
 		} else if (!strcmp(argv[i], "-4")) {
+#ifdef DHCPv6
 			if (local_family_set && (local_family != AF_INET)) {
 				log_fatal("Server cannot run in both IPv4 and "
 					  "IPv6 mode at the same time.");