Throw errors for nested targets in GN.

tools/gn/function_toolchain.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <algorithm>
 #include <limits>
 
 #include "tools/gn/err.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/parse_tree.h"
@@ skipping 283 matching lines @@
     "      is_32bit = true\n"
     "      is_64bit = false\n"
     "    }\n"
     "  }\n";
 
 Value RunToolchain(Scope* scope,
                    const FunctionCallNode* function,
                    const std::vector<Value>& args,
                    BlockNode* block,
                    Err* err) {
+  NonNestableBlock non_nestable(scope, function, "toolchain");
+  if (!non_nestable.Enter(err))
+    return Value();
+
   if (!EnsureNotProcessingImport(function, scope, err) ||
       !EnsureNotProcessingBuildConfig(function, scope, err))
     return Value();
 
   // Note that we don't want to use MakeLabelForScope since that will include
   // the toolchain name in the label, and toolchain labels don't themselves
   // have toolchain names.
   const SourceDir& input_dir = scope->GetSourceDir();
   Label label(input_dir, args[0].string_value());
   if (g_scheduler->verbose_logging())
@@ skipping 631 matching lines @@
     return Value();
 
   Scope::KeyValueMap values;
   block_scope.GetCurrentScopeValues(&values);
   toolchain->args() = values;
 
   return Value();
 }
 
 }  // namespace functions