Build libmonochrome.so with secondary toolchain

build/config/android/secondary_abi.gni

+# Copyright 2016 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.
+
+# This file contains common secondary abi config for the Android build.
+
+if (target_os == "android") {
+  if (target_cpu == "arm64" || target_cpu == "x64" || target_cpu == "mips64el") {
+    android_64bit_target_cpu = true
+  } else if (target_cpu == "arm" || target_cpu == "x86" ||
+             target_cpu == "mipsel") {
+    android_64bit_target_cpu = false
+  } else {
+    assert(false, "Unknown target CPU: $target_cpu")
+  }
+
+  # Intentionally do not define android_app_secondary_abi_cpu for 32-bit
+  # target_cpu, since they are not used.
+  if (target_cpu == "arm64") {
+    android_secondary_abi_cpu = "arm"
+  } else if (target_cpu == "x64") {
+    android_secondary_abi_cpu = "x86"
+  } else if (target_cpu == "mips64el") {
+    android_secondary_abi_cpu = "mipsel"
+  }
+
+  if (defined(android_secondary_abi_cpu)) {
+    _android_secondary_abi_cpu_with_v8 =
+        "${android_secondary_abi_cpu}_v8_${android_secondary_abi_cpu}"
+    if (is_clang) {
+      android_secondary_abi_toolchain = "//build/toolchain/android:clang_${_android_secondary_abi_cpu_with_v8}"
+    } else {
+      android_secondary_abi_toolchain =
+          "//build/toolchain/android:${_android_secondary_abi_cpu_with_v8}"
+    }
+  }
+}