Use llvm-opt's LTO pass list instead of generic O2/O3 pass list for LTO

tests/toolchain/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('env')
 
 # force inclusion of entire library, so that we can validate it
 # NOTE: This approach does not work for -lc because of tons of
 #       undefined symbols which would have to be stubbed out
@@ skipping 270 matching lines @@
 
 
 # Test that local variable dwarf info is preserved with linking and LTO.
 # Force '-g' on in case it was not turned on for some reason, and lower
 # optimization settings to prevent some optimizations that would convert
 # locals from llvm allocas to registers.
 # We may be able to remove this test once LLVM has an upstream regression test.
 debug_env = env.Clone()
 debug_env.Append(CFLAGS=['-g', '-O0'])
 debug_env.Append(CCFLAGS=['-g', '-O0'])
+debug_env.Append(LINKFLAGS=['-O0'])
 dwarf_local_var_nexe = debug_env.ComponentProgram('dwarf_local_var',
                                                   ['dwarf_local_var.c',
                                                    'dwarf_local_var_dummy.c'],
                                                   EXTRA_LIBS=['${NONIRT_LIBS}'])
 # Sanity-check -- make sure it runs.
 node = debug_env.CommandSelLdrTestNacl('dwarf_local_var_run.out',
                                        dwarf_local_var_nexe,
                                        exit_status=55)
 debug_env.AddNodeToTestSuite(node,
                              ['toolchain_tests', 'small_tests'],
@@ skipping 25 matching lines @@
   opt_env.Append(CCFLAGS=['-O3'])
   opt_env.Append(LINKFLAGS=['-O3'])
   obj = unopt_env.ComponentObject('printf_to_puts.c')
   nexe = opt_env.ComponentProgram('printf_to_puts',
                                   obj,
                                   EXTRA_LIBS=['${NONIRT_LIBS}'])
   node = env.CommandSelLdrTestNacl('printf_to_puts.out', nexe)
   env.AddNodeToTestSuite(node,
                          ['toolchain_tests', 'small_tests'],
                          'run_printf_to_puts_test')