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/env.c

@@ -38,7 +38,7 @@ extern char **environ;
 static const char env_longopts[] =
 	"ignore-environment\0" No_argument       "i"
 	"unset\0"              Required_argument "u"
-	"\0";
+	;
 #endif
 
 int env_main(int argc, char** argv);