Enhance GN's "desc" command to support configs.

tools/gn/switches.cc

 // 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.
 
 #include "tools/gn/switches.h"
 
 namespace switches {
 
 const char kArgs[] = "args";
 const char kArgs_HelpShort[] =
@@ skipping 207 matching lines @@
     "  This will spew logging events to the console for debugging issues.\n"
     "  Good luck!\n";
 
 const char kVersion[] = "version";
 const char kVersion_HelpShort[] =
     "--version: Prints the GN version number and exits.";
 // It's impossible to see this since gn_main prints the version and exits
 // immediately if this switch is used.
 const char kVersion_Help[] = "";
 
+const char kAllToolchains[] = "all-toolchains";
+
 // -----------------------------------------------------------------------------
 
 SwitchInfo::SwitchInfo()
     : short_help(""),
       long_help("") {
 }
 
 SwitchInfo::SwitchInfo(const char* short_help, const char* long_help)
     : short_help(short_help),
       long_help(long_help) {
@@ skipping 19 matching lines @@
     INSERT_VARIABLE(Tracelog)
     INSERT_VARIABLE(Verbose)
     INSERT_VARIABLE(Version)
   }
   return info_map;
 }
 
 #undef INSERT_VARIABLE
 
 }  // namespace switches