IRT: Replace __attribute__((constructor)) with explicit call in _start()

src/untrusted/irt/irt.gyp

 # 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.
 
 {
   'includes': [
     '../../../build/common.gypi',
   ],
   'variables': {
     'irt_sources': [
 # irt_support_sources
-      'irt_core_entry.c',
       'irt_entry.c',
       'irt_malloc.c',
       'irt_private_pthread.c',
       'irt_private_tls.c',
 # irt_common_interfaces
       'irt_basic.c',
       'irt_fdio.c',
       'irt_filename.c',
       'irt_memory.c',
       'irt_dyncode.c',
@@ skipping 85 matching lines @@
           'sources': [ 'aeabi_read_tp.S' ],
         }],
       ],
       'dependencies': [
         '<(DEPTH)/native_client/tools.gyp:prep_toolchain',
         '<(DEPTH)/native_client/src/untrusted/nacl/nacl.gyp:nacl_lib_newlib',
       ],
     },
   ],
 }