Make GN build work on Mac again.

tools/gn/secondary/third_party/nss/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/linux/pkg_config.gni")
 
 if (is_linux) {
   # This is a dependency on NSS with no libssl. On Linux we use a built-in SSL
   # library but the system NSS libraries. Non-Linux platforms using NSS use the
   # hermetic one in //third_party/nss.
@@ skipping 122 matching lines @@
       "nspr/pr/src/io/prprf.c",
       "nspr/pr/src/io/prscanf.c",
       "nspr/pr/src/io/prsocket.c",
       "nspr/pr/src/io/prstdio.c",
       "nspr/pr/src/linking/prlink.c",
       "nspr/pr/src/malloc/prmalloc.c",
       "nspr/pr/src/malloc/prmem.c",
       "nspr/pr/src/md/prosdep.c",
       "nspr/pr/src/md/unix/darwin.c",
       "nspr/pr/src/md/unix/os_Darwin.s",
-      # os_Darwin_x86.s and os_Darwin_x86_64.s are included by
-      # os_Darwin.s.
-      "nspr/pr/src/md/unix/os_Darwin_x86.s",
-      "nspr/pr/src/md/unix/os_Darwin_x86_64.s",
       "nspr/pr/src/md/unix/unix.c",
       "nspr/pr/src/md/unix/unix_errors.c",
       "nspr/pr/src/md/unix/uxproces.c",
       "nspr/pr/src/md/unix/uxrng.c",
       "nspr/pr/src/md/unix/uxshm.c",
       "nspr/pr/src/md/unix/uxwrap.c",
       "nspr/pr/src/md/windows/ntgc.c",
       "nspr/pr/src/md/windows/ntinrval.c",
       "nspr/pr/src/md/windows/ntmisc.c",
       "nspr/pr/src/md/windows/ntsec.c",
@@ skipping 997 matching lines @@
 
     deps = [
       ":nspr",
       "//third_party/sqlite",
     ]
 
     forward_dependent_configs_from = [ ":nspr" ]
   }
 }  # Windows/Mac/iOS.