Build only the appropriate x86 arches for nacl (chrome side).

build/common_untrusted.gypi

 # Copyright (c) 2012 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.
 
 # This GYP file should be included for every target in Chromium that is built
 # using the NaCl toolchain.
 {
   'includes': [
     '../native_client/build/untrusted.gypi',
   ],
   'target_defaults': {
     'conditions': [
+      # TODO(bradnelson): Drop this once the nacl side does the same.
+      ['target_arch=="x64"', {
+        'variables': {
+          'enable_x86_32': 0,
+        },
+      }],
+      ['target_arch=="ia32" and OS!="win"', {
+        'variables': {
+          'enable_x86_64': 0,
+        },
+      }],
       ['target_arch=="arm"', {
         'variables': {
           'clang': 1,
         },
         'defines': [
           # Needed by build/build_config.h processor architecture detection.
           '__ARMEL__',
           # Needed by base/third_party/nspr/prtime.cc.
           '__arm__',
           # Disable ValGrind. The assembly code it generates causes the build
           # to fail.
           'NVALGRIND',
         ],
       }],
     ],
   },
-}
+}