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

third_party/zlib/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.
 
 config("zlib_config") {
   include_dirs = [ "." ]
 }
 
 static_library("zlib_x86_simd") {
-  if (!is_ios && (cpu_arch == "x86" || cpu_arch == "x64")) {
+  if (!is_ios && (current_cpu == "x86" || current_cpu == "x64")) {
     sources = [
       "crc_folding.c",
       "fill_window_sse.c",
     ]
     if (!is_win || is_clang) {
       cflags = [
         "-msse4.2",
         "-mpclmul",
       ]
     }
@@ skipping 37 matching lines @@
     "trees.c",
     "trees.h",
     "uncompr.c",
     "x86.h",
     "zconf.h",
     "zlib.h",
     "zutil.c",
     "zutil.h",
   ]
 
-  if (!is_ios && (cpu_arch == "x86" || cpu_arch == "x64")) {
+  if (!is_ios && (current_cpu == "x86" || current_cpu == "x64")) {
     sources += [ "x86.c" ]
   }
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
 
   public_configs = [ ":zlib_config" ]
   deps = [
     ":zlib_x86_simd",
   ]
@@ skipping 44 matching lines @@
     "google/zip_internal.cc",
     "google/zip_internal.h",
     "google/zip_reader.cc",
     "google/zip_reader.h",
   ]
   deps = [
     ":minizip",
     "//base",
   ]
 }