Reset LIBPATH to fix the build of MIPS nacl_helper_bootstrap on Ubuntu Precise

src/trusted/service_runtime/build.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 platform
 import os
 
 Import('env')
 
@@ skipping 426 matching lines @@
   # a "build environment" environment.  We need to compile this program
   # with native defaults for where we're being built, i.e. for x86-64
   # when the host is x86-64 but platform=x86-32.
   munge_env = env.Clone(BUILD_TYPE='gen',
                         BUILD_TYPE_DESCRIPTION='build-host generation',
                         NACL_BUILD_FAMILY='TRUSTED_BUILD',
                         CC='cc',
                         LINK='${CC}',
                         CCFLAGS=['-O2'],
                         LINKFLAGS=[],
-                        )
+                        LIBPATH=[])
   bootstrap_munge = munge_env.Program(
       'nacl_bootstrap_munge_phdr',
       ['linux/nacl_bootstrap_munge_phdr.c'],
       LIBS=['elf'])
 
   bootstrap_prog = bootstrap_env.Command(
       'nacl_helper_bootstrap',
       [bootstrap_env.File('linux/nacl_bootstrap_munge_phdr.py'),
        bootstrap_munge, bootstrap_raw],
       '${PYTHON} ${SOURCES} ${TARGET}'
@@ skipping 550 matching lines @@
 node = env.CommandTest(
   'nacl_error_log_test.out',
   command=[exe],
   exit_status=expected_exit,
   filter_regex='"(NaClCrashLogWriter.*)|(This is a test of the emergency.*)"',
   filter_group_only='true',
   stdout_golden=env.File('nacl_error_log_test.stdout'))
 
 env.AddNodeToTestSuite(node, ['small_tests'],
                        'run_nacl_error_log_test')