Cleanup: Use Bit('build_ARCH') instead of Bit('target_ARCH')

tests/gdb/nacl.scons

 # -*- python -*-
 # Copyright (c) 2012 The Native Client 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 os
 
 Import('env')
 
 if 'TRUSTED_ENV' not in env:
   Return()
 
 if env.UnderWindowsCoverage():
   Return()
 
-if env.Bit('build_arm') or env.Bit('target_mips32'):
+if env.Bit('build_arm') or env.Bit('build_mips32'):
   if env.UsingEmulator():
     # nacl-gdb is built with ARM support but not MIPS support.
     if env.Bit('build_mips32'):
       Return()
     nacl_x86_toolchain_dir = env.GetToolchainDir(target_arch='x86',
                                                  is_pnacl=False,
                                                  lib_name='newlib')
     nacl_gdb_path = os.path.join(nacl_x86_toolchain_dir, 'bin', 'i686-nacl-gdb')
     env.Replace(GDB=nacl_gdb_path)
   else:
@@ skipping 134 matching lines @@
 # work on qemu-arm.
 AddGdbTest('break_continue_thread', is_thread_test=True,
            is_broken=env.UsingEmulator())
 
 AddGdbTest('syscall_thread', is_thread_test=True)
 
 # We don't run this test on non-x86 architectures or PNaCl since it
 # contains inline assembly.
 if env.Bit('build_x86') and not env.Bit('bitcode'):
   AddGdbTest('mmap')