Eliminate spurious warning, convert to getopt, and eliminate redundant check.
diff --git a/gunzip.c b/gunzip.c
index e6f6bdf..b4edb25 100644
--- a/gunzip.c
+++ b/gunzip.c
@@ -91,7 +91,7 @@
 	if (strcmp(applet_name, "zcat") == 0)
 		flags |= gunzip_to_stdout;
 
-	while ((opt = getopt(argc, argv, "ctfh")) != -1) {
+	while ((opt = getopt(argc, argv, "ctfhd")) != -1) {
 		switch (opt) {
 		case 'c':
 			flags |= gunzip_to_stdout;
@@ -102,6 +102,8 @@
 		case 't':
 			flags |= gunzip_test;
 			break;
+		case 'd': /* Used to convert gzip to gunzip. */
+			break;
 		case 'h':
 		default:
 			show_usage(); /* exit's inside usage */