GN: Check if targets with precompiled headers use unsupported toolchains.

tools/gn/ninja_binary_target_writer.h

 // 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.
 
 #ifndef TOOLS_GN_NINJA_BINARY_TARGET_WRITER_H_
 #define TOOLS_GN_NINJA_BINARY_TARGET_WRITER_H_
 
 #include "base/macros.h"
 #include "tools/gn/config_values.h"
 #include "tools/gn/ninja_target_writer.h"
 #include "tools/gn/toolchain.h"
 #include "tools/gn/unique_vector.h"
 
 struct EscapeOptions;
 class SourceFileTypeSet;
 
 // Writes a .ninja file for a binary target type (an executable, a shared
 // library, or a static library).
 class NinjaBinaryTargetWriter : public NinjaTargetWriter {
  public:
-  class SourceFileTypeSet;
-
   NinjaBinaryTargetWriter(const Target* target, std::ostream& out);
   ~NinjaBinaryTargetWriter() override;
 
   void Run() override;
 
  private:
   typedef std::set<OutputFile> OutputFileSet;
 
   // Writes all flags for the compiler: includes, defines, cflags, etc.
   void WriteCompilerVars(const SourceFileTypeSet& used_types);
@@ skipping 117 matching lines @@
   const Tool* tool_;
 
   // Cached version of the prefix used for rule types for this toolchain.
   std::string rule_prefix_;
 
   DISALLOW_COPY_AND_ASSIGN(NinjaBinaryTargetWriter);
 };
 
 #endif  // TOOLS_GN_NINJA_BINARY_TARGET_WRITER_H_