Ashwini Sharma pointed out that my previous tweak to [!abc] groups still didn't get the error reporting right (test case "touch -d 12 -r f2 f1"). This says "no 'r' with 'd'" for that, and still shouldn't be able to fall off the end of the list (segfault) because an option can't conflict with itself (that's what the ~(1<<i) on lib/args.c line 317 is for).

// Included after toys.h, for network stuff.  Some build environments
// don't include network support, so we shouldn't include it unless we're
// going to build it.

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <poll.h>