[build] Add //third_party/android_tools BUILD file needed by zlib

Change-Id: I4f641bcc4940ab508f38b32397455f996659784b
Reviewed-on: https://dart-review.googlesource.com/c/81363
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Zach Anderson <zra@google.com>
Auto-Submit: Vyacheslav Egorov <vegorov@google.com>
Reviewed-by: Zach Anderson <zra@google.com>

build/secondary/third_party/android_tools/BUILD.gn

@@ -0,0 +1,29 @@
+# Copyright 2018 The Dart project 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/android/config.gni")
+
+config("cpu_features_include") {
+  include_dirs = [ "$android_ndk_root/sources/android/cpufeatures" ]
+}
+
+config("cpu_features_warnings") {
+  if (is_clang) {
+    # cpu-features.c has few unused functions on x86 b/26403333
+    cflags = [ "-Wno-unused-function" ]
+  }
+}
+
+source_set("cpu_features") {
+  sources = [
+    "$android_ndk_root/sources/android/cpufeatures/cpu-features.c",
+  ]
+  public_configs = [ ":cpu_features_include" ]
+  configs -= [ "//build/config/compiler:chromium_code" ]
+  configs += [
+    "//build/config/compiler:no_chromium_code",
+    # Must be after no_chromium_code for warning flags to be ordered correctly.
+    ":cpu_features_warnings",
+  ]
+}