Fix with -fno-common
https://github.com/fgont/ipv6toolkit/commit/2bde90f3845234490549640dc6ed5712d84969ba

Index: tools/scan6.c
--- tools/scan6.c.orig
+++ tools/scan6.c
@@ -251,8 +251,8 @@ uint16_t				service_ports_dec[]={21, 22, 23, 25, 49, 5
 
 
 /* IPv6 Address Resolution */
-sigjmp_buf				env;
-unsigned int			canjump;
+static sigjmp_buf				env;
+static unsigned int				canjump;
 
 int main(int argc, char **argv){
 	extern char				*optarg;