GN: Set arm_float_abi when target_cpu = "arm64"

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 (current_cpu == "arm") {
   declare_args() {
     # Version of the ARM processor when compiling on ARM. Ignored on non-ARM
     # platforms.
     arm_version = 7
 
@@ skipping 55 matching lines @@
     }
 
     arm_use_thumb = true
 
     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"
 }