fix getopt[_long] clobbering of optopt on success

getopt is only specified to modify optopt on error, and some software
apparently infers an error from optopt!=0.

getopt_long is changed analogously. the resulting behavior differs
slightly from the behavior of the GNU implementation of getopt_long,
which keeps an internal shadow copy of optopt and copies it to the
public one on return, but since the GNU implementation also exhibits
this shadow-copy behavior for plain getopt where is is non-conforming,
I think this can reasonably be considered a bug rather than an
intentional behavior that merits mimicing.

src/misc/getopt.c

@@ -60,7 +60,6 @@ int getopt(int argc, char * const argv[], const char *optstring)
 		c = 0xfffd; /* replacement char */
 	}
 	optchar = argv[optind]+optpos;
-	optopt = c;
 	optpos += k;
 
 	if (!argv[optind][optpos]) {
@@ -79,6 +78,7 @@ int getopt(int argc, char * const argv[], const char *optstring)
 	} while (l && d != c);
 
 	if (d != c) {
+		optopt = c;
 		if (optstring[0] != ':' && opterr)
 			__getopt_msg(argv[0], ": unrecognized option: ", optchar, k);
 		return '?';
@@ -86,6 +86,7 @@ int getopt(int argc, char * const argv[], const char *optstring)
 	if (optstring[i] == ':') {
 		if (optstring[i+1] == ':') optarg = 0;
 		else if (optind >= argc) {
+			optopt = c;
 			if (optstring[0] == ':') return ':';
 			if (opterr) __getopt_msg(argv[0],
 				": option requires an argument: ",

src/misc/getopt_long.c

@@ -75,9 +75,9 @@ static int __getopt_long_core(int argc, char *const *argv, const char *optstring
 		if (cnt==1) {
 			i = match;
 			optind++;
-			optopt = longopts[i].val;
 			if (*opt == '=') {
 				if (!longopts[i].has_arg) {
+					optopt = longopts[i].val;
 					if (colon || !opterr)
 						return '?';
 					__getopt_msg(argv[0],
@@ -89,6 +89,7 @@ static int __getopt_long_core(int argc, char *const *argv, const char *optstring
 				optarg = opt+1;
 			} else if (longopts[i].has_arg == required_argument) {
 				if (!(optarg = argv[optind])) {
+					optopt = longopts[i].val;
 					if (colon) return ':';
 					if (!opterr) return '?';
 					__getopt_msg(argv[0],
@@ -107,6 +108,7 @@ static int __getopt_long_core(int argc, char *const *argv, const char *optstring
 			return longopts[i].val;
 		}
 		if (argv[optind][1] == '-') {
+			optopt = 0;
 			if (!colon && opterr)
 				__getopt_msg(argv[0], cnt ?
 					": option is ambiguous: " :