Make GN Android build link executables

third_party/ashmem/BUILD.gn

+# 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.
+
+assert(is_android)
+
+import("//build/config/android/config.gni")
+
+if (is_android_webview_build) {
+  # WebView build uses the Android system version of ashmem to avoid linking
+  # problems.
+  group("ashmem") {
+    assert(false, "Implement system ashmem for webview build")
+  }
+} else {
+  source_set("ashmem") {
+    sources = [
+      "ashmem.h",
+      "ashmem-dev.c",
+    ]
+  }
+}