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

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 6774b2a36b68419ac0e649da0b3292ff3e15647b..efa4a3a2a5e0d9a5d4433c07c34b7a58bfc4d0e0 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -1059,11 +1059,6 @@ config("default_warnings") {
       # 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
@@ -1073,6 +1068,15 @@ config("default_warnings") {
       "-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

[Lei Zhang, 2017/03/31 00:55:52]

Missing crbug.com/

[Nico, 2017/03/31 01:22:59]

D'oh, will fix in follow up

+        "-Wno-deprecated-register",
+      ]
+    }
+
     # Chrome's hermetic Clang compiler, NaCl's Clang compiler and Xcode's Clang
     # compiler will almost always have different versions. Certain flags may not
     # be recognized by one version or the other.