[MIPS] Small updates after LLVM merge

[MIPS] Small updates after LLVM merge

The change includes several small fixes:

1. set registers $at and $gp to zero when switching to untrusted code to
   avoid leaks from trusted code;
2. ignore MIPS reginfo section (generated with recently merged trunk code)
3. info message for the MIPS toolchain should print "nacl_sdk" to reflect
   recent changes in the toolchain script.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=2275
TEST= run smoke tests


Committed: http://src.chromium.org/viewvc/native_client?view=rev&revision=11151

[Mark Seaborn, 2013-04-08 21:51:25]

LGTM

[commit-bot: I haz the power, 2013-04-08 21:56:21]

CQ is trying da patch. Follow status at
https://nativeclient-status.appspot.com/cq/petarj@mips.com/13454020/1

[commit-bot: I haz the power, 2013-04-08 21:56:23]

Presubmit check for 13454020-1 failed and returned exit status 1.

INFO:root:Found 4 file(s).
Running presubmit commit checks ...
Running /b/commit-queue/workdir/nacl/PRESUBMIT.py

** Presubmit Warnings **
License must match:
.*? Copyright (\(c\) )?(2013|2012|2011|2010|2009|2008|2007|2006|2006-2008) The
Native Client Authors\. All rights reserved\.\n.*? Use of this source code is
governed by a BSD-style license that can be\n.*? found in the LICENSE file\.(?:
\*/)?\n
Found a bad license header in these files:
  src/include/elf_constants.h

[commit-bot: I haz the power, 2013-04-08 22:27:26]

CQ is trying da patch. Follow status at
https://nativeclient-status.appspot.com/cq/petarj@mips.com/13454020/22001

[commit-bot: I haz the power, 2013-04-09 15:30:41]

Change committed as 11151