Land prep work to enable NaCl in the Linux x64 GN builds.

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 530 matching lines @@
   }
   if (is_chromeos && cros_use_custom_toolchain) {
     set_default_toolchain("//build/toolchain/cros:target")
   }
 } else if (is_mac) {
   host_toolchain = "//build/toolchain/mac:clang"
   set_default_toolchain(host_toolchain)
 } else if (is_ios) {
   host_toolchain = "//build/toolchain/mac:host_clang"
   set_default_toolchain("//build/toolchain/mac:clang")
+} else if (is_nacl) {
+  # TODO(GYP): This will need to change when we get NaCl working
+  # on multiple platforms, but this whole block of code (how we define
+  # host_toolchain) needs to be reworked regardless to key off of build_os
+  # and build_cpu_arch rather than the is_* variables.
+  host_toolchain = "//build/toolchain/linux:clang_x64"
 }
 
 # ==============================================================================
 # COMPONENT SETUP
 # ==============================================================================
 
 # TODO(brettw) erase this once the built-in "component" function is removed.
 if (is_component_build) {
   component_mode = "shared_library"
 } else {
@@ skipping 189 matching lines @@
       }
       if (defined(invoker.testonly)) {
         testonly = invoker.testonly
       }
       if (defined(invoker.visibility)) {
         visibility = invoker.visibility
       }
     }
   }
 }