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

debianutils/run_parts.c

@@ -44,7 +44,7 @@ static const char runparts_longopts[] =
 //TODO: "reverse\0" No_argument       "r"
 //TODO: "verbose\0" No_argument       "v"
 #endif
-	"\0";
+	;
 #endif
 
 struct globals {