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

third_party/opus/BUILD.gn

 # 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.
 
 import("//build/config/arm.gni")
 import("//testing/test.gni")
 
 # If fixed point implementation shall be used (otherwise float).
-use_opus_fixed_point = cpu_arch == "arm" || cpu_arch == "arm64"
+use_opus_fixed_point = current_cpu == "arm" || current_cpu == "arm64"
 
 # If ARM optimizations shall be used to accelerate performance.
-use_opus_arm_optimization = cpu_arch == "arm"
+use_opus_arm_optimization = current_cpu == "arm"
 
 # If OPUS Run Time CPU Detections (RTCD) shall be used.
 # Based on the conditions in celt/arm/armcpu.c:
 # defined(_MSC_VER) || defined(__linux__).
-use_opus_rtcd = cpu_arch == "arm" && (is_win || is_android || is_linux)
+use_opus_rtcd = current_cpu == "arm" && (is_win || is_android || is_linux)
 
 config("opus_config") {
   include_dirs = [ "src/include" ]
 }
 
 config("opus_test_config") {
   include_dirs = [
     "src/celt",
     "src/silk",
   ]
@@ skipping 62 matching lines @@
       "VAR_ARRAYS",
     ]
   }
 
   if (is_posix && !is_android) {
     # Suppress a warning given by opus_decoder.c that tells us
     # optimizations are turned off.
     cflags = [ "-Wno-#pragma-messages" ]
   }
 
-  if (!is_debug && is_posix && (cpu_arch == "arm" || cpu_arch == "arm64")) {
+  if (!is_debug && is_posix &&
+      (current_cpu == "arm" || current_cpu == "arm64")) {
     configs -= [ "//build/config/compiler:optimize" ]
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 
   if (use_opus_fixed_point) {
     sources += gypi_values.opus_fixed_sources
 
     defines += [ "FIXED_POINT" ]
 
     include_dirs += [ "src/silk/fixed" ]
@@ skipping 140 matching lines @@
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     "//build/config/compiler:no_chromium_code",
     ":opus_test_config",
   ]
 
   deps = [
     ":opus",
   ]
 }