rdisc: tell in --version output if ENABLE_RDISC_SERVER was defined

Manual page tells some functionality is conditional to configure option, so
inform in version output what can be expected.

Reviewed-by: Petr Vorel <pvorel@suse.cz>
Tested-by: Petr Vorel <pvorel@suse.cz>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>

rdisc.c

@@ -323,6 +323,13 @@ int main(int argc, char **argv)
 				break;
 			case 'V':
 				printf(IPUTILS_VERSION("rdisc"));
+				printf("Compiled %s ENABLE_RDISC_SERVER.\n",
+#ifdef RDISC_SERVER
+						"with"
+#else
+						"without"
+#endif
+				);
 				exit(0);
 #ifdef RDISC_SERVER
 			case 'T':