Update Chomium's build files to work w/ latest GN binaries.

components/nacl/nacl_defines.gni

 # 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.
 
 nacl_defines = []
 if (is_win) {
   nacl_defines += [
     "NACL_WINDOWS=1",
     "NACL_LINUX=0",
     "NACL_OSX=0",
@@ skipping 17 matching lines @@
 
 if (is_android) {
   nacl_defines += [
     "NACL_WINDOWS=0",
     "NACL_LINUX=1",
     "NACL_OSX=0",
     "NACL_ANDROID=1",
   ]
 }
 
-if (cpu_arch == "x86") {
+if (current_cpu == "x86") {
   nacl_defines += [
     "NACL_BUILD_SUBARCH=32",
     "NACL_BUILD_ARCH=x86",
   ]
-} else if (cpu_arch == "x64") {
+} else if (current_cpu == "x64") {
   nacl_defines += [
     "NACL_BUILD_SUBARCH=64",
     "NACL_BUILD_ARCH=x86",
   ]
-} else if (cpu_arch == "arm") {
+} else if (current_cpu == "arm") {
   nacl_defines += [
     "NACL_BUILD_ARCH=arm",
     "NACL_BUILD_SUBARCH=32",
   ]
-} else if (cpu_arch == "mipsel") {
+} else if (current_cpu == "mipsel") {
   nacl_defines += [
     "NACL_BUILD_ARCH=mips",
     "NACL_BUILD_SUBARCH=32",
   ]
 }