GN: Allow setting the path to Python

tools/gn/switches.h

 // Copyright 2014 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_SWITCHES_H_
 #define TOOLS_GN_SWITCHES_H_
 
 #include <map>
 
 #include "base/strings/string_piece.h"
@@ skipping 34 matching lines @@
 extern const char kFailOnUnusedArgs_Help[];
 
 extern const char kMarkdown[];
 extern const char kMarkdown_HelpShort[];
 extern const char kMarkdown_Help[];
 
 extern const char kNoColor[];
 extern const char kNoColor_HelpShort[];
 extern const char kNoColor_Help[];
 
+extern const char kScriptExecutable[];
+extern const char kScriptExecutable_HelpShort[];
+extern const char kScriptExecutable_Help[];
+
 extern const char kQuiet[];
 extern const char kQuiet_HelpShort[];
 extern const char kQuiet_Help[];
 
 extern const char kRoot[];
 extern const char kRoot_HelpShort[];
 extern const char kRoot_Help[];
 
 extern const char kRuntimeDepsListFile[];
 extern const char kRuntimeDepsListFile_HelpShort[];
@@ skipping 15 matching lines @@
 extern const char kVerbose_HelpShort[];
 extern const char kVerbose_Help[];
 
 extern const char kVersion[];
 extern const char kVersion_HelpShort[];
 extern const char kVersion_Help[];
 
 }  // namespace switches
 
 #endif  // TOOLS_GN_SWITCHES_H_