Build PPAPI NaCl Glibc tests with GN

build/config/nacl/config.gni

Index: build/config/nacl/config.gni
diff --git a/build/config/nacl/config.gni b/build/config/nacl/config.gni
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+# Copyright 2015 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.
+
+declare_args() {
+  # Native Client supports both Newlib and Glibc C libraries where Newlib
+  # is assumed to be the default one; use this to determine whether Glibc
+  # is being used instead.
+  is_nacl_glibc = false
+}