NaCl: Remove the only use of NACL_ARCH_CPU_* #defines

ppapi/native_client/src/trusted/plugin/arch_x86/sandbox_isa.cc

 // 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.
 
 #include "native_client/src/trusted/plugin/nexe_arch.h"
 #include "native_client/src/trusted/platform_qualify/nacl_os_qualify.h"
 
 namespace {
 // The list of supported ISA strings for x86.  See issue:
 //   http://code.google.com/p/nativeclient/issues/detail?id=1040 for more
 // information.  Note that these string are to be case-insensitive compared.
 const char* const kNexeArchX86_32 = "x86-32";
 const char* const kNexeArchX86_64 = "x86-64";
 }  // namespace
 
 namespace plugin {
 const char* GetSandboxISA() {
-#if defined(NACL_ARCH_CPU_X86_64) && (defined(NACL_LINUX) || defined(NACL_OSX))
+#if (NACL_ARCH(NACL_BUILD_ARCH) == NACL_x86 && NACL_BUILD_SUBARCH == 64) && \
+    (defined(NACL_LINUX) || defined(NACL_OSX))
   return kNexeArchX86_64;  // 64-bit Linux or Mac.
 #else
   return NaClOsIs64BitWindows() == 1
       ? kNexeArchX86_64  // 64-bit Windows (Chrome, Firefox)
       : kNexeArchX86_32;  // everything else.
 #endif
 }
 }  // namespace plugin