coroutines: Handle lambda closure pointers like 'this'.

It was agreed amongst the implementors that the correct
interpretation of the standard is that lambda closure pointers
should be treated in the same manner as class object pointers.

gcc/cp/ChangeLog:

	* coroutines.cc (instantiate_coro_traits): Pass a reference
	to lambda closure objects to traits instantiation.
	(morph_fn_to_coro): Likewise for promise parameter
	preview and allocator lookup.

(cherry picked from commit 1c140cfbfa4b465a29ef26f1fdfef04c671e3c9c)

gcc/cp/coroutines.cc

@@ -297,15 +297,14 @@ instantiate_coro_traits (tree fndecl, location_t kw)
 
   tree functyp = TREE_TYPE (fndecl);
   tree arg = DECL_ARGUMENTS (fndecl);
-  bool lambda_p = LAMBDA_FUNCTION_P (fndecl);
   tree arg_node = TYPE_ARG_TYPES (functyp);
   tree argtypes = make_tree_vec (list_length (arg_node)-1);
   unsigned p = 0;
 
   while (arg_node != NULL_TREE && !VOID_TYPE_P (TREE_VALUE (arg_node)))
     {
-      /* See PR94807, as to why we must exclude lambda here.  */
-      if (is_this_parameter (arg) && !lambda_p)
+      if (is_this_parameter (arg)
+	  || DECL_NAME (arg) == closure_identifier)
 	{
 	  /* We pass a reference to *this to the param preview.  */
 	  tree ct = TREE_TYPE (TREE_TYPE (arg));
@@ -3963,9 +3962,7 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
 	{
 	  param_info *parm_i = param_uses->get (arg);
 	  gcc_checking_assert (parm_i);
-	  if (parm_i->lambda_cobj)
-	    vec_safe_push (args, arg);
-	  else if (parm_i->this_ptr)
+	  if (parm_i->this_ptr || parm_i->lambda_cobj)
 	    {
 	      /* We pass a reference to *this to the allocator lookup.  */
 	      tree tt = TREE_TYPE (TREE_TYPE (arg));
@@ -4169,9 +4166,7 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
 
 	  /* Add this to the promise CTOR arguments list, accounting for
 	     refs and special handling for method this ptr.  */
-	  if (parm.lambda_cobj)
-	    vec_safe_push (promise_args, arg);
-	  else if (parm.this_ptr)
+	  if (parm.this_ptr || parm.lambda_cobj)
 	    {
 	      /* We pass a reference to *this to the param preview.  */
 	      tree tt = TREE_TYPE (arg);