Replace #define syscalls cancel machinery.

nptl/sysdeps/pthread/createthread.c

 /* Copyright (C) 2002-2007, 2008 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
 
    The GNU C Library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.
 
    The GNU C Library is distributed in the hope that it will be useful,
@@ skipping 60 matching lines @@
      we momentarily store a false value; this doesn't matter because there
      is no kosher thing a signal handler interrupting us right here can do
      that cares whether the thread count is correct.  */
   atomic_increment (&__nptl_nthreads);
 
 #ifndef __native_client__
 #error "This code was changed to work only in Native Client"
 #endif
 
   /* Native Client does not have a notion of a thread ID, so we make
-     one up.  This must be positive to mark the thread as not
-     exited.  */
-  pd->tid = ((unsigned int) pd) >> 2;
+     one up.  This must be small enough to leave space for number identifying
+     the clock.  Use CLOCK_IDFIELD_SIZE to guarantee that.  */
+  pd->tid = ((unsigned int) pd) >> CLOCK_IDFIELD_SIZE;
 
   /* Native Client syscall thread_create does not push return address onto stack
      as opposed to the kernel.  We emulate this behavior on x86-64 to meet the
      ABI requirement ((%rsp + 8) mod 16 == 0).  On x86-32 the attribute
      'force_align_arg_pointer' does the same for start_thread ().  */
 #ifdef __x86_64__
   STACK_VARIABLES_ARGS -= 8;
 #endif
 
   if (__nacl_irt_thread_create (fct, STACK_VARIABLES_ARGS, pd) != 0)
@@ skipping 172 matching lines @@
   /* Actually create the thread.  */
   int res = do_clone (pd, attr, clone_flags, start_thread,
                       STACK_VARIABLES_ARGS, stopped);
 
   if (res == 0 && stopped)
     /* And finally restart the new thread.  */
     lll_unlock (pd->lock, LLL_PRIVATE);
 
   return res;
 }