testsuite: Add c23-stdarg-4.c test variant where all functions return large struct

testsuite: Add c23-stdarg-4.c test variant where all functions return large struct

I think we have no coverage for the case where structure_value_addr_parm and
TYPE_NO_NAMED_ARGS_STDARG_P are both true.  The
  if (type_arg_types != 0)
    n_named_args
      = (list_length (type_arg_types)
         /* Count the struct value address, if it is passed as a parm.  */
         + structure_value_addr_parm);
  else if (TYPE_NO_NAMED_ARGS_STDARG_P (funtype))
    n_named_args = 0;
  else
    /* If we know nothing, treat all args as named.  */
    n_named_args = num_actuals;
code should probably have n_named_args = structure_value_addr_parm;
instead of n_named_args = 0;, this testcase is an attempt to see if
it is broken on any target.

2024-02-28  Jakub Jelinek  <jakub@redhat.com>

	* gcc.dg/c23-stdarg-6.c: New test.

(cherry picked from commit dc30e24b76d570e13a71567a38f7594b104736bf)