GN: Declare ARM build arguments for either target_cpu or current_cpu == "arm"

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.
 
-if (target_cpu == "arm") {
+# These are primarily relevant in current_cpu == "arm" contexts, where
+# ARM code is being compiled.  But they can also be relevant in the
+# host toolchain context when target_cpu == "arm", where a host-side
+# build tool being built will change its behavior depending on the
+# details of the target configuration.
+if (target_cpu == "arm" || 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 44 matching lines @@
     if (arm_use_neon) {
       arm_fpu = "neon"
     } else {
       arm_fpu = "vfpv3-d16"
     }
   }
 } else if (current_cpu == "arm64") {
   # arm64 supports only "hard".
   arm_float_abi = "hard"
 }