clang/win: use clang_warning_flags, like mac and linux do

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 5333 matching lines @@
                   '-fmsc-version=1800',
                   '/fallback',
 
                   # Many files use intrinsics without including this header.
                   # TODO(hans): Fix those files, or move this to sub-GYPs.
                   '/FIIntrin.h',
 
                   # TODO(hans): Make this list shorter eventually.
                   '-Qunused-arguments',
                   '-Wno-c++11-compat-deprecated-writable-strings',
-                  '-Wno-char-subscripts',
                   '-Wno-deprecated-declarations',
-                  '-Wno-deprecated-register',
                   '-Wno-empty-body',
                   '-Wno-enum-conversion',
                   '-Wno-extra-tokens',
                   '-Wno-ignored-attributes',
                   '-Wno-incompatible-pointer-types',
                   '-Wno-int-to-void-pointer-cast',
                   '-Wno-invalid-noreturn',
                   '-Wno-logical-op-parentheses',
                   '-Wno-microsoft',
                   '-Wno-missing-braces',
@@ skipping 264 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }