GN: Work on Linux build defines

tools/gn/command_help.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 <iostream>
 
 #include "tools/gn/args.h"
 #include "tools/gn/commands.h"
 #include "tools/gn/err.h"
@@ skipping 12 matching lines @@
 void PrintToplevelHelp() {
   OutputString("Commands (type \"gn help <command>\" for more details):\n");
 
   const commands::CommandInfoMap& command_map = commands::GetCommands();
   for (commands::CommandInfoMap::const_iterator i = command_map.begin();
        i != command_map.end(); ++i)
     PrintShortHelp(i->second.help_short);
 
   OutputString(
       "\n"
-      "  When run with no arguments \"gn gen\" is assumed.\n"
-      "\n"
       "Common switches:\n");
   PrintShortHelp(
       "--args: Specifies build arguments overrides. "
       "See \"gn help buildargs\".");
   PrintShortHelp(
       "--no-exec: Skips exec_script calls (for performance testing).");
   PrintShortHelp(
       "-q: Quiet mode, don't print anything on success.");
   PrintShortHelp(
       "--output: Directory for build output (relative to source root).");
@@ skipping 125 matching lines @@
     return 0;
   }
 
   // No help on this.
   Err(Location(), "No help on \"" + args[0] + "\".").PrintToStdout();
   RunHelp(std::vector<std::string>());
   return 1;
 }
 
 }  // namespace commands