Remove GN forwarding of the target variables.

build/toolchain/gcc_toolchain.gni

 # 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.
 
 import("//build/config/clang/clang.gni")
 import("//build/config/nacl/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/v8_target_cpu.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/goma.gni")
@@ skipping 81 matching lines @@
            "toolchain_args must specify a current_cpu")
     assert(defined(invoker_toolchain_args.current_os),
            "toolchain_args must specify a current_os")
 
     # When invoking this toolchain not as the default one, these args will be
     # passed to the build. They are ignored when this is the default toolchain.
     toolchain_args = {
       # Populate toolchain args from the invoker.
       forward_variables_from(invoker_toolchain_args, "*")
 
-      # These values need to be passed through unchanged to all secondary
-      # toolchains. BUILDCONFIG.gn sets some defaults based on the values of
-      # the operating system and compiler, and we want to force the values to
-      # be consistent if re-running the computation in another context leads
-      # to different defaults.
+      # The host toolchain value computed by the default toolchain's setup
+      # needs to be passed through unchanged to all secondary toolchains to
+      # ensure that it's always the same, regardless of the values that may be
+      # set on those toolchains.
       host_toolchain = host_toolchain
-      target_os = target_os
-      target_cpu = target_cpu
 
       if (!defined(invoker_toolchain_args.v8_current_cpu)) {
         v8_current_cpu = invoker_toolchain_args.current_cpu
       }
     }
 
     # When the invoker has explicitly overridden use_goma or cc_wrapper in the
     # toolchain args, use those values, otherwise default to the global one.
     # This works because the only reasonable override that toolchains might
     # supply for these values are to force-disable them.
@@ skipping 371 matching lines @@
     if (defined(invoker.use_debug_fission)) {
       assert(!defined(toolchain_args.use_debug_fission))
       toolchain_args.use_debug_fission = invoker.use_debug_fission
     }
     if (defined(invoker.use_gold)) {
       assert(!defined(toolchain_args.use_gold))
       toolchain_args.use_gold = invoker.use_gold
     }
   }
 }