Merge Mike Roe's binutils change for recent CHERI ISA updates:

  commit c83fe667fdc404c83da1ed5ae4d473d6145ca044
  Author: Michael Roe <mroe@cornstalk.org.uk>
  Date:   Fri Feb 14 21:08:26 2014 +0000

    Added new cfromptr instruction. Changed the syntax of ccleartag.

Changes to use the new CClearTag syntax will be merged to CheriBSD
shortly; in the interim there will be a short window of unbuildability.
Remove now-unused CHERI_CLOADORCLEAR() from libcheri -- no
longer required now that we require compiler support.
Update mips/include/cheri.h for new and modified CHERI
assembler: CClearTag syntax change, CGetDefault, CSetDefault,
CCheckType, CCheckPerm, CToPtr, and CFromPtr.
Use new CClearTag syntax: clear the tag from the current value
of the register.  We will probably want to use CFromPtr(NULL)
here in the future to fully clear capability-register values,
but I don't yet have a bitfile that supports that.
Update another instance of CClearTag.
Use Clang builtin for CGetDefault rather than direct capability-register
access.  Eliminates a couple of warnings about $c0 use, as well as some
inline assembly.
For now, don't error out on warnings when building cheritest.
Don't misimplement CHERI_CGETDEFAULT; also, it never requires a memory
clobber regardless of target register.
Tweaks to cheritest to make it more friendly to revised warnings about $c0
use (which become errors under clang).
Use $idc, which is unsealed, instead of co.co_datacap, which is sealed,
when looking at object-instance data in cheri_fd methods.

(Unfortunately, this triggers a compiler crash when using the CHERI
Clang/LLVM builtin for querying $idc.)
Workaround Clang bug involving the $idc copmiler builtin by instead
using inline assembly to query its value.
Un-ifdef more of cheri_fd_enter() now that there is a workaround for the
$idc-related crash.
NO_WERROR is no longer required for libcheri.
In cheri_fd test code, use cheri_ptr() explicitly to
properly bound lengths; don't use 'const' where we don't
mean to, since that won't work.