coroutines: Ensure distinct DTOR trees [PR95137].

Part of the PR notes that there are UBSAN fails for the coroutines
test suite.  These are primarily related to the use of the same DTOR
tree in the two edges from the await block.  Fixed by building a new
tree for each.

gcc/cp/ChangeLog:

	PR c++/95137
	* coroutines.cc (expand_one_await_expression): Build separate
	DTOR trees for the awaitable object on the destroy and resume
	paths.

(cherry picked from commit 006f28aefeb3be575239beddc7febe56dff463a2)

gcc/cp/coroutines.cc

@@ -1490,19 +1490,13 @@ expand_one_await_expression (tree *stmt, tree *await_expr, void *d)
   tree resume_label = create_named_label_with_ctx (loc, buf, actor);
   tree empty_list = build_empty_stmt (loc);
 
-  tree dtor = NULL_TREE;
   tree await_type = TREE_TYPE (var);
-  if (needs_dtor)
-    dtor = build_special_member_call (var, complete_dtor_identifier, NULL,
-				      await_type, LOOKUP_NORMAL,
-				      tf_warning_or_error);
-
   tree stmt_list = NULL;
   tree t_expr = STRIP_NOPS (expr);
   tree r;
   tree *await_init = NULL;
   if (t_expr == var)
-    dtor = NULL_TREE;
+    needs_dtor = false;
   else
     {
       /* Initialize the var from the provided 'o' expression.  */
@@ -1617,7 +1611,12 @@ expand_one_await_expression (tree *stmt, tree *await_expr, void *d)
   destroy_label = build_stmt (loc, LABEL_EXPR, destroy_label);
   append_to_statement_list (destroy_label, &body_list);
   if (needs_dtor)
-    append_to_statement_list (dtor, &body_list);
+    {
+      tree dtor = build_special_member_call (var, complete_dtor_identifier,
+					     NULL, await_type, LOOKUP_NORMAL,
+					     tf_warning_or_error);
+      append_to_statement_list (dtor, &body_list);
+    }
   r = build1_loc (loc, GOTO_EXPR, void_type_node, data->cleanup);
   append_to_statement_list (r, &body_list);
 
@@ -1652,7 +1651,12 @@ expand_one_await_expression (tree *stmt, tree *await_expr, void *d)
   /* Get a pointer to the revised statment.  */
   tree *revised = tsi_stmt_ptr (tsi_last (stmt_list));
   if (needs_dtor)
-    append_to_statement_list (dtor, &stmt_list);
+    {
+      tree dtor = build_special_member_call (var, complete_dtor_identifier,
+					     NULL, await_type, LOOKUP_NORMAL,
+					     tf_warning_or_error);
+      append_to_statement_list (dtor, &stmt_list);
+    }
   data->index += 2;
 
   /* Replace the original statement with the expansion.  */