GN build improvements.

tools/gn/secondary/third_party/snappy/BUILD.gn

-# Copyright (c) 2013 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.
-
-config("snappy_config") {
-  include_dirs = [
-    "src",
-  ]
-
-  # These OS-specific generated headers were made by running the configure
-  # script offline.
-  if (is_win) {
-    include_dirs += [ "win32" ]
-  } else if (is_mac) {
-    include_dirs += [ "mac" ]
-  } else {
-    include_dirs += [ "linux" ]
-  }
-}
-
-static_library("snappy") {
-  sources = [
-    "src/snappy-internal.h",
-    "src/snappy-sinksource.cc",
-    "src/snappy-sinksource.h",
-    "src/snappy-stubs-internal.cc",
-    "src/snappy-stubs-internal.h",
-    "src/snappy.cc",
-    "src/snappy.h",
-  ]
-
-  configs -= [ "//build/config/compiler:chromium_code" ]
-  configs += [ "//build/config/compiler:no_chromium_code" ]
-  direct_dependent_configs = [ ":snappy_config" ]
-
-  if (is_clang) {
-    # snappy-stubs-internal.h unapologetically has: using namespace std
-    # https://code.google.com/p/snappy/issues/detail?id=70
-    configs -= [ "//build/config/clang:extra_warnings" ]
-  }
-
-  if (is_win) {
-    # https://code.google.com/p/snappy/issues/detail?id=75
-    cflags = [ "/wd4267" ]  # Conversion from size_t to 'type'.
-  }
-}