Reverse Poptrap instructions before Return (#3924)

* Reverse the instruction sequence at the end of pop_all
* Reenable checking top trap vs popped handler

Author: gretay-js

backend/select_utils.ml

@@ -147,7 +147,7 @@ let pop_all_traps env =
     | Operation.Uncaught -> acc
     | Operation.Specific_trap (lbl, t) -> pop_all (Pop lbl :: acc) t
   in
-  pop_all [] env.trap_stack
+  pop_all [] env.trap_stack |> List.rev
 
 let env_create ~tailrec_label =
   { vars = V.Map.empty;
@@ -508,7 +508,7 @@ module Stack_offset_and_exn = struct
           InstructionId.format instr.id
       | top_trap :: traps ->
         (* CR-soon gyorsh: investigate why this check sometimes fails. *)
-        if false && not (Label.equal lbl_handler top_trap)
+        if not (Label.equal lbl_handler top_trap)
         then
           Misc.fatal_errorf
             "Cfgize.Stack_offset_and_exn.process_basic: poptrap label %a does \