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

build/config/arm.gni

Index: build/config/arm.gni
diff --git a/build/config/arm.gni b/build/config/arm.gni
index 326a49ece16530816b979cacec9e70b265284c1b..bd8e71c2d22c28f7242e24a4456acf177f4015b1 100644
--- a/build/config/arm.gni
+++ b/build/config/arm.gni
@@ -2,13 +2,11 @@
 # 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.
@@ -87,7 +85,7 @@ if (current_cpu == "arm" || v8_target_cpu == "arm") {
       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