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

archival/tar.c

@@ -752,7 +752,7 @@ static const char tar_longopts[] =
 # if ENABLE_FEATURE_TAR_FROM
 	"exclude\0"             Required_argument "\xff"
 # endif
-	"\0";
+	;
 #endif
 
 int tar_main(int argc, char **argv);