[Ada] Fix visibility inside declare_expression

The first implementation just created a scope for the analysis of the
declarations and the expression, so that visibility would just work as
it does for all other constructs. However this led to an annoying bug
when one of the declarations or the expression itself creates a
transient scope: there may be a confusion on scope exit between those
two scopes. As a result visibility is handled by explicit traversal of
the expression and replacement of occurrences of the local variables,
see Replace_Local_Ref in Resolve_Declare_Expression (sem_res.adb). The
current code does not take into account that there may be references to
a local object in a subsequent declaration (not just in the expression).

gcc/ada/

	* sem_res.adb (Resolve_Declare_Expression): Traverse the
	expression to replace references to local variables that occur
	within declarations of the declare_expression; fix typos in
	comments.

gcc/ada/sem_res.adb

@@ -7595,7 +7595,7 @@ package body Sem_Res is
       Local : Entity_Id := Empty;
 
       function Replace_Local (N  : Node_Id) return Traverse_Result;
-      --  Use a tree traversal to replace each ocurrence of the name of
+      --  Use a tree traversal to replace each occurrence of the name of
       --  a local object declared in the construct, with the corresponding
       --  entity. This replaces the usual way to perform name capture by
       --  visibility, because it is not possible to place on the scope
@@ -7632,7 +7632,7 @@ package body Sem_Res is
 
       procedure Replace_Local_Ref is new Traverse_Proc (Replace_Local);
 
-      --  Start of processing for  Resolve_Declare_Expression
+   --  Start of processing for Resolve_Declare_Expression
 
    begin
 
@@ -7645,6 +7645,19 @@ package body Sem_Res is
          then
             Local := Defining_Identifier (Decl);
             Replace_Local_Ref (Expr);
+
+            --  Traverse the expression to replace references to local
+            --  variables that occur within declarations of the
+            --  declare_expression.
+
+            declare
+               D : Node_Id := Next (Decl);
+            begin
+               while Present (D) loop
+                  Replace_Local_Ref (D);
+                  Next (D);
+               end loop;
+            end;
          end if;
 
          Next (Decl);