win/clang: Turn on -Wignored-pragmas again

build/config/compiler/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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 927 matching lines @@
 
     # Building with Clang on Windows is a work in progress and very
     # experimental. See crbug.com/82385.
     # Keep this in sync with the similar block in build/common.gypi
     if (is_clang) {
       cflags += [
         # TODO(hans): Make this list shorter eventually, http://crbug.com/504657
         "-Wno-microsoft-enum-value",  # http://crbug.com/505296
         "-Wno-unknown-pragmas",  # http://crbug.com/505314
         "-Wno-microsoft-cast",  # http://crbug.com/550065
-        "-Wno-ignored-pragmas",  # http://crbug.com/644841
       ]
     }
   } else {
     if (is_mac && !is_nacl) {
       # When compiling Objective-C, warns if a method is used whose
       # availability is newer than the deployment target. This is not
       # required when compiling Chrome for iOS.
       cflags += [ "-Wpartial-availability" ]
     }
 
@@ skipping 655 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }