[gn] Move build to gypfiles

gypfiles/set_clang_warning_flags.gypi

 # Copyright 2016 the V8 project authors. All rights reserved.
 # Copyright (c) 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.
 
 # This file is meant to be included to set clang-specific compiler flags.
 # To use this the following variable can be defined:
 #   clang_warning_flags:       list: Compiler flags to pass to clang.
 #   clang_warning_flags_unset: list: Compiler flags to not pass to clang.
 #
@@ skipping 39 matching lines @@
     ['clang==0 and host_clang==1', {
       'target_conditions': [
         ['_toolset=="host"', {
           'cflags': [ '>@(clang_warning_flags)' ],
           'cflags!': [ '>@(clang_warning_flags_unset)' ],
         }],
       ],
     }],
   ],
 }