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

build/config/win/BUILD.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.
 
 import("//build/config/win/visual_studio_version.gni")
 
 # Compiler setup for the Windows SDK. Applied to all targets.
 config("sdk") {
   # The include path is the stuff returned by the script.
   #include_dirs = msvc_config[0]  TODO(brettw) make this work.
@@ skipping 13 matching lines @@
 # targets need to manually override it for their compiles.
 config("winver") {
   defines = [
     "_WIN32_WINNT=0x0603",
     "WINVER=0x0603",
   ]
 }
 
 # Linker flags for Windows SDK setup, this is applied only to EXEs and DLLs.
 config("sdk_link") {
-  if (cpu_arch == "x64") {
+  if (current_cpu == "x64") {
     ldflags = [ "/MACHINE:X64" ]
     lib_dirs = [
       "$windows_sdk_path\Lib\winv6.3\um\x64",
       "$visual_studio_path\VC\lib\amd64",
       "$visual_studio_path\VC\atlmfc\lib\amd64",
     ]
   } else {
     ldflags = [
       "/MACHINE:X86",
       "/SAFESEH",  # Not compatible with x64 so use only for x86.
@@ skipping 86 matching lines @@
 
 # Nominmax --------------------------------------------------------------------
 
 # Some third party code defines NOMINMAX before including windows.h, which
 # then causes warnings when it's been previously defined on the command line.
 # For such targets, this config can be removed.
 
 config("nominmax") {
   defines = [ "NOMINMAX" ]
 }