Enable -Wdeprecated-register (except on CrOS and 32-bit Linux).

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/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
@@ skipping 1046 matching lines @@
       # This warns on using ints as initializers for floats in
       # initializer lists (e.g. |int a = f(); CGSize s = { a, a };|),
       # which happens in several places in chrome code. Not sure if
       # this is worth fixing.
       "-Wno-c++11-narrowing",
 
       # Warns on switches on enums that cover all enum values but
       # also contain a default: branch. Chrome is full of that.
       "-Wno-covered-switch-default",
 
-      # Clang considers the `register` keyword as deprecated, but e.g.
-      # code generated by flex (used in angle) contains that keyword.
-      # http://crbug.com/255186
-      "-Wno-deprecated-register",
-
       # TODO(thakis): This used to be implied by -Wno-unused-function,
       # which we no longer use. Check if it makes sense to remove
       # this as well. http://crbug.com/316352
       "-Wno-unneeded-internal-declaration",
 
       # TODO(hans): Get this cleaned up, http://crbug.com/428099
       "-Wno-inconsistent-missing-override",
     ]
 
+    if (is_chromeos || (is_linux && target_cpu == "x86")) {
+      cflags += [
+        # TODO(thakis): Figure out why CrOS needs this, fix, remove.
+        # https://crbug.com/806812
+        # TODO(thakis): Remove from 32-bit Linux eventually, https://707084
+        "-Wno-deprecated-register",
+      ]
+    }
+
     # use_xcode_clang only refers to the iOS toolchain, host binaries use
     # chromium's clang always.
     if (!is_nacl && (!use_xcode_clang || current_toolchain == host_toolchain)) {
       # Flags NaCl (Clang 3.7) and Xcode 7.3 (Clang clang-703.0.31) do not
       # recognize.
       cflags += [
         # TODO(thakis): https://crbug.com/604888
         "-Wno-undefined-var-template",
 
         # TODO(thakis): https://crbug.com/617318
@@ skipping 618 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
   }
 }