Add gyp files to build NSS in Dart

runtime/tools/gyp/third_party_configurations.gypi

+# Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+# for details. All rights reserved. Use of this source code is governed by a
+# BSD-style license that can be found in the LICENSE file.
+

[Mads Ager (google), 2012/10/31 09:01:01]

Could we call this file nss_configurations.gypi to make it clearer what it is
used for? I find the third_party name a bit too generic.

Let's add a comment here instead of in the variables section describing what
this file is used for. Also, add a comment that this file should only be used
for compiling C and not C++ code.

+{
+  'variables': {
+    # Used by third_party/nss, which is from Chromium.
+    'os_posix': 1,
+    'os_bsd': 0,
+    'chromeos': 0,
+    'clang': 0,
+  },
+  'target_defaults': {
+    'cflags': [
+      '-Wno-unused-variable',
+      '-Wno-unused-but-set-variable',
+      '-Wno-missing-field-initializers',
+      '-Wno-uninitialized',
+      '-Wno-sign-compare',
+      '-Wno-empty-body',
+      '-Wno-type-limits',
+      '-Wno-pointer-to-int-cast',
+      '-UHAVE_CVAR_BUILT_ON_SEM',
+    ],
+    'cflags!': [

[Mads Ager (google), 2012/10/31 09:01:01]

I would like some more comments here. There is one line that has a comment. I
got confused by -fno-exceptions being removed until I realized that this is for
compiling C code and not C++.

+      '-Werror',
+      '-Wall',
+      '-Wvla',
+      '-Woverloaded-virtual',
+      '-ansi',
+      '-fno-exceptions',
+      '-fvisibility=hidden',
+      # Not supported for C, only for C++.
+      '-Wnon-virtual-dtor',
+      '-Wno-conversion-null',
+      '-fno-rtti',
+      '-fvisibility-inlines-hidden',
+    ],
+    'configurations': {
+      'Dart_Base': {
+        'xcode_settings': {
+          # Remove 'ansi' setting.
+          'GCC_C_LANGUAGE_STANDARD': '',
+          'GCC_TREAT_WARNINGS_AS_ERRORS': 'NO', # -Werror off
+        },
+      },
+    },
+  },
+}