Implement arflags in the GN build.

build/config/posix/BUILD.gn

 # Copyright 2015 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/sanitizers/sanitizers.gni")
 import("//build/config/sysroot.gni")
+import("//build/toolchain/toolchain.gni")
 
 assert(is_posix)
 
+# This is included by reference in the //build/config/compiler config that
+# is applied to all Posix targets. It is here to separate out the logic that is
+# Posix-only. Note that this is in addition to an OS-specific variant of this
+# config.
+config("compiler") {
+  if ((allow_posix_link_time_opt || is_cfi) && !is_nacl) {
+    arflags = [
+      "--plugin",
+      rebase_path("//third_party/llvm-build/Release+Asserts/lib/LLVMgold.so",
+                  root_build_dir),
+    ]
+  }
+}
+
 # This is included by reference in the //build/config/compiler:runtime_library
 # config that is applied to all targets. It is here to separate out the logic
 # that is Posix-only. Please see that target for advice on what should go in
 # :runtime_library vs. :compiler.
 config("runtime_library") {
   if (!is_mac && !is_ios && sysroot != "") {
     # Pass the sysroot to all C compiler variants, the assembler, and linker.
     cflags = [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]
     asmflags = cflags
     ldflags = cflags
 
     # Need to get some linker flags out of the sysroot.
     ldflags += [ exec_script("sysroot_ld_path.py",
                              [
                                rebase_path("//build/linux/sysroot_ld_path.sh",
                                            root_build_dir),
                                sysroot,
                              ],
                              "value") ]
   }
 }