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/install.c

@@ -28,7 +28,7 @@ static const char install_longopts[] =
 	"preserve_context\0"    No_argument       "\xff"
 	"preserve-context\0"    No_argument       "\xff"
 #endif
-	"\0";
+	;
 #endif