Update GN build to use v8_target_cpu instead of v8_target_arch.

gni/v8.gni

 # Copyright 2016 the V8 project 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/sanitizers/sanitizers.gni")
+import("//build/config/v8_target_cpu.gni")
 
 declare_args() {
   # Turns on compiler optimizations in V8 in Debug build.
   v8_optimized_debug = true
 
   # Enable the snapshot feature, for fast context creation.
   # http://v8project.blogspot.com/2015/09/custom-startup-snapshots.html
   v8_use_snapshot = true
 
   # Use external files for startup data blobs:
   # the JS builtins sources and the start snapshot.
   v8_use_external_startup_data = !is_ios
-
-  # V8 generates code for this architecture. If v8_target_arch differs from
-  # target_cpu, a simulator will be run.
-  v8_target_arch = ""
-}
-
-if (v8_target_arch == "") {
-  if (is_msan) {
-    # Running the V8-generated code on an ARM simulator is a powerful hack that
-    # allows the tool to see the memory accesses from JITted code. Without this
-    # flag, JS code causes false positive reports from MSan.
-    v8_target_arch = "arm64"
-  } else {
-    v8_target_arch = target_cpu
-  }
 }
 
 ###############################################################################
 # Templates
 #
 
 # Points to // in v8 stand-alone or to //v8/ in chromium. We need absolute
 # paths for all configs in templates as they are shared in different
 # subdirectories.
 path_prefix = get_path_info("../", "abspath")
@@ skipping 34 matching lines @@
 }
 
 template("v8_component") {
   component(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= remove_configs
     configs += add_configs
   }
 }