lookip: Explicitly include string.h for strcpy()

src/libcharon/plugins/lookip/lookip.c

@@ -22,6 +22,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <errno.h>
 #include <getopt.h>
 #include <arpa/inet.h>