Fixed warnings in tao_idl generated code

Classes that have a pure virtual member cannot be constructed as the
most-derived type of an object.  Their constructors are always called
indirectly from derived constructors.  Initializing virtual bases in
these constructors is effectively dead code since virtual bases can only
be initialized by the most-derived type.  Some compilers, with some
warning settings, generated warnings for this.

TAO/TAO_IDL/be/be_interface.cpp

@@ -2234,7 +2234,7 @@ be_interface::copy_ctor_helper (be_interface *derived,
 {
   // We can't call ourselves in a copy constructor, and
   // abstract interfaces don't exist on the skeleton side.
-  if (derived == base || base->is_abstract ())
+  if (derived == base || base->is_abstract () || derived->nmembers () > 0)
     {
       return 0;
     }

TAO/TAO_IDL/be/be_visitor_interface/amh_ss.cpp

@@ -200,7 +200,7 @@ TAO_IDL_Copy_Ctor_Worker::emit (be_interface *derived,
       TAO_OutStream *os,
       be_interface *base)
 {
-  if (derived == base)
+  if (derived == base || derived->nmembers () > 0)
     {
       return 0;
     }

TAO/TAO_IDL/be/be_visitor_interface/interface_ss.cpp

@@ -107,25 +107,37 @@ be_visitor_interface_ss::visit_interface (be_interface *node)
 
   *os << full_skel_name << "::"
       << local_name_prefix << node_local_name
-      << " ()" << be_idt_nl;
+      << " ()";
 
-  *os << ": TAO_ServantBase ()" << be_uidt_nl;
+  bool const init_bases = node->nmembers () == 0;
+  if (init_bases)
+    {
+      *os << be_idt_nl << ": TAO_ServantBase ()" << be_uidt_nl;
+    }
+  else
+    {
+      *os << be_nl;
+    }
 
   // Default constructor body.
   *os << "{" << be_idt_nl
-      << "this->optable_ = std::addressof(tao_" << flat_name
+      << "this->optable_ = std::addressof (tao_" << flat_name
       << "_optable);" << be_uidt_nl
       << "}" << be_nl_2;
 
   // find if we are at the top scope or inside some module
   *os << full_skel_name << "::"
       << local_name_prefix << node_local_name << " ("
       << "const " << local_name_prefix
-      << node_local_name << "& rhs)";
+      << node_local_name << " &"
+      << (init_bases ? "rhs" : "") << ")";
 
-  *os << be_idt_nl
-      << ": TAO_Abstract_ServantBase (rhs)," << be_nl
-      << "  TAO_ServantBase (rhs)";
+  if (init_bases)
+    {
+      *os << be_idt_nl
+          << ": TAO_Abstract_ServantBase (rhs)," << be_nl
+          << "  TAO_ServantBase (rhs)";
+    }
 
   if (this->generate_copy_ctor (node, os) == -1)
     {