client: fix parsing of -v command option

The sources and sourcestats commands accept -v as an option, but the
glibc implementation of getopt() reorders the arguments and parses the
option as a command-line option of chronyc.

Add '+' to the getopt string to disable this feature. Other getopt()
implementations should consider it a new command-line option, which will
be handled as an error if present.

client.c

@@ -3143,7 +3143,7 @@ main(int argc, char **argv)
   optind = 1;
 
   /* Parse short command-line options */
-  while ((opt = getopt(argc, argv, "46acdf:h:mnp:v")) != -1) {
+  while ((opt = getopt(argc, argv, "+46acdf:h:mnp:v")) != -1) {
     switch (opt) {
       case '4':
       case '6':