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

coreutils/ls.c

@@ -122,7 +122,7 @@ static smallint show_color;
  * equivalent */
 static const char ls_color_opt[] =
 	"color\0" Optional_argument "\xff" /* no short equivalent */
-	"\0";
+	;
 #else
 enum { show_color = 0 };
 #endif