flambda-backend: Fix uses of polymorphic comparison in Flambda 2 (#2312)

* Add -open Int_replace_polymorphic_compare for flambda2

* Remove explicit opens of Int_replace_polymorphic_compare

* Fix occurrences of polymorphic comparison

Author: mshinwell

lambda/debuginfo.ml

@@ -27,6 +27,19 @@ module Scoped_location = struct
     | Sc_partial_or_eta_wrapper
     | Sc_lazy
 
+  let equal_scope_item si1 si2 =
+    match si1, si2 with
+    | Sc_anonymous_function, Sc_anonymous_function
+    | Sc_value_definition, Sc_value_definition
+    | Sc_module_definition, Sc_module_definition
+    | Sc_class_definition, Sc_class_definition
+    | Sc_method_definition, Sc_method_definition
+    | Sc_partial_or_eta_wrapper, Sc_partial_or_eta_wrapper
+    | Sc_lazy, Sc_lazy -> true
+    | (Sc_anonymous_function | Sc_value_definition | Sc_module_definition
+      | Sc_class_definition | Sc_method_definition | Sc_partial_or_eta_wrapper
+      | Sc_lazy), _ -> false
+
   type scopes =
     | Empty
     | Cons of {item: scope_item; str: string; str_fun: string; name : string; prev: scopes;

lambda/debuginfo.mli

@@ -23,6 +23,8 @@ module Scoped_location : sig
     | Sc_partial_or_eta_wrapper
     | Sc_lazy
 
+  val equal_scope_item : scope_item -> scope_item -> bool
+
   type scopes = private
     | Empty
     | Cons of {item: scope_item; str: string; str_fun: string; name : string; prev: scopes;