Fix the output of "gn args" for the OS and CPU architecture.

tools/gn/secondary/build/config/BUILDCONFIG.gn

 # 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.
 
 # =============================================================================
 # BUILD FLAGS
 # =============================================================================
 #
 # This block lists input arguments to the build, along with their default
 # values. GN requires listing them explicitly so it can validate input and have
@@ skipping 16 matching lines @@
   # Component build.
   is_component_build = false
   # Debug build.
   is_debug = true
 
   # Set to true when compiling with the Clang compiler. Typically this is used
   # to configure warnings.
   is_clang = false
 
   # ASH is enabled.
+  # TODO(brettw) this should be moved out of the main build config file.
   use_ash = false
   # Aura is enabled.
+  # TODO(brettw) this should be moved out of the main build config file.
   use_aura = false
   # Ozone is enabled.
+  # TODO(brettw) this should be moved out of the main build config file.
   use_ozone = false
 }
 
 # =============================================================================
 # OS DEFINITIONS
 # =============================================================================
 #
 # We set these various is_FOO booleans for convenience in writing OS-based
 # conditions.
 #
@@ skipping 320 matching lines @@
     # Special toolchain for ARM cross-compiling.
     set_default_toolchain("//build/toolchain/linux:arm-cross-compile")
   } else {
     # Use whatever GCC is on the current platform.
     set_default_toolchain(host_toolchain)
   }
 } else if (is_mac) {
   host_toolchain = "//build/toolchain/mac:clang"
   set_default_toolchain(host_toolchain)
 }