tile: fix DWARF bug in clone() for created thread

Previously, we would see a bad frame in the gdb backtrace output, e.g.:

  (gdb) bt
  #0  foo () at foo.c:5
  #1  0x000000aaaab68ee8 in start_thread () from /lib/libpthread.so.0
  #2  0x000000aaaad01c88 in clone () from /lib/libc.so.6
  #3  0x0000000000000000 in ?? ()

With this change the bogus frame #3 is gone and we have the
same output as x86 does for the same program.

ports/ChangeLog.tile

@@ -1,3 +1,7 @@
+2012-12-14  Chris Metcalf  <cmetcalf@tilera.com>
+
+	* sysdeps/unix/sysv/linux/tile/nptl/clone.S: Fix DWARF info.
+
 2012-11-29  Chris Metcalf  <cmetcalf@tilera.com>
 
 	* sysdeps/tile/s_fmaf.c: Remove redundant #defines now provided

ports/sysdeps/unix/sysv/linux/tile/nptl/clone.S

@@ -160,14 +160,15 @@ ENTRY (__clone)
    r32: the user function pointer  */
 
 .Lthread_start:
+	cfi_def_cfa_offset (FRAME_SIZE)
+	cfi_undefined (lr)
 	/* Check and see if we need to reset the PID, which we do if
 	   CLONE_THREAD isn't set, i.e. we're not staying in the thread group.
 	   If CLONE_VM is set, we're doing some kind of thread-like clone,
 	   so we set the tid/pid to -1 to disable using the cached values
 	   in getpid().  Otherwise (if CLONE_VM isn't set), it's a
 	   fork-like clone, and we go ahead and write the cached values
 	   from the true system pid (retrieved via __NR_getpid syscall).  */
-	cfi_def_cfa_offset (FRAME_SIZE)
 #ifdef __tilegx__
 	{
 	 moveli r0, hw1_last(CLONE_VM)