Replace index_in_[sub]str_array with index_in_[sub]strings,

which scans thru "abc\0def\0123\0\0" type strings. Saves 250 bytes.

   text    data     bss     dec     hex filename
 781266    1328   11844  794438   c1f46 busybox_old
 781010    1328   11844  794182   c1e46 busybox_unstripped

util-linux/getopt.c

@@ -276,7 +276,7 @@ static const char getopt_longopts[] =
 	"unquoted\0"     No_argument       "u"
 	"alternative\0"  No_argument       "a"
 	"name\0"         Required_argument "n"
-	"\0";
+	;
 #endif
 
 int getopt_main(int argc, char *argv[]);