Add gcc toolchain for arm64/linux

build/toolchain/linux/BUILD.gn

 # Copyright 2013 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/sysroot.gni")
 import("//build/toolchain/gcc_toolchain.gni")
 
 clang_toolchain("clang_arm") {
   toolprefix = "arm-linux-gnueabihf-"
   toolchain_args = {
     current_cpu = "arm"
     current_os = "linux"
   }
 }
 
 clang_toolchain("clang_arm64") {
   toolprefix = "aarch64-linux-gnu-"
   toolchain_args = {
     current_cpu = "arm64"
     current_os = "linux"
   }
 }
 
+gcc_toolchain("arm64") {
+  toolprefix = "aarch64-linux-gnu-"
+
+  cc = "${toolprefix}gcc"
+  cxx = "${toolprefix}g++"
+
+  ar = "${toolprefix}ar"
+  ld = cxx
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
+
+  toolchain_args = {
+    current_cpu = "arm64"
+    current_os = "linux"
+    is_clang = false
+  }
+}
+
 gcc_toolchain("arm") {
   toolprefix = "arm-linux-gnueabihf-"
 
   cc = "${toolprefix}gcc"
   cxx = "${toolprefix}g++"
 
   ar = "${toolprefix}ar"
   ld = cxx
   readelf = "${toolprefix}readelf"
   nm = "${toolprefix}nm"
@@ skipping 99 matching lines @@
   nm = "mipsel-linux-gnu-nm"
 
   toolchain_args = {
     cc_wrapper = ""
     current_cpu = "mipsel"
     current_os = "linux"
     is_clang = false
     use_goma = false
   }
 }