Land chromium-side work to clean up handling of v8_target_cpu in the GN build.

build/config/arm.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.
 
 import("//build/config/v8_target_cpu.gni")
 
 # These are primarily relevant in current_cpu == "arm" contexts, where
 # ARM code is being compiled.  But they can also be relevant in the
 # other contexts when the code will change its behavior based on the
 # cpu it wants to generate code for.
-if (current_cpu == "arm" || v8_target_cpu == "arm") {
+if (current_cpu == "arm" || v8_current_cpu == "arm") {
   declare_args() {
     # Version of the ARM processor when compiling on ARM. Ignored on non-ARM
     # platforms.
     arm_version = 7
 
     # The ARM floating point mode. This is either the string "hard", "soft", or
     # "softfp". An empty string means to use the default one for the
     # arm_version.
     arm_float_abi = ""
 
@@ skipping 58 matching lines @@
         arm_float_abi = "hard"
       }
     }
 
     if (arm_use_neon) {
       arm_fpu = "neon"
     } else {
       arm_fpu = "vfpv3-d16"
     }
   }
-} else if (current_cpu == "arm64" || v8_target_cpu == "arm64") {
+} else if (current_cpu == "arm64" || v8_current_cpu == "arm64") {
   # arm64 supports only "hard".
   arm_float_abi = "hard"
   arm_use_neon = true
 }