compiler: build a single backend type for type alias

    
    A type alias and its underlying type are identical. Build a
    single backend type for them. Previously we build two backend
    types, which sometimes confuse the backend's type system.
    
    Also don't include type aliases into the list of named type
    declarations, since they are not named types.
    
    Reviewed-on: https://go-review.googlesource.com/123362

From-SVN: r262572

gcc/go/gofrontend/MERGE

-ea7ac7784791dca517b6681a02c39c11bf136755
+267686fd1dffbc03e610e9f17dadb4e72c75f18d
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/gogo.cc

@@ -7604,7 +7604,7 @@ Named_object::get_backend(Gogo* gogo, std::vector<Bexpression*>& const_decls,
     case NAMED_OBJECT_TYPE:
       {
         Named_type* named_type = this->u_.type_value;
-	if (!Gogo::is_erroneous_name(this->name_))
+	if (!Gogo::is_erroneous_name(this->name_) && !named_type->is_alias())
 	  type_decls.push_back(named_type->get_backend(gogo));
 
         // We need to produce a type descriptor for every named

gcc/go/gofrontend/types.cc

@@ -991,6 +991,11 @@ Type::get_backend(Gogo* gogo)
   if (this->btype_ != NULL)
     return this->btype_;
 
+  if (this->named_type() != NULL && this->named_type()->is_alias()) {
+    this->btype_ = this->unalias()->get_backend(gogo);
+    return this->btype_;
+  }
+
   if (this->forward_declaration_type() != NULL
       || this->named_type() != NULL)
     return this->get_btype_without_hash(gogo);