Initial ISA 2.07 support for POWER8-tuned libc

The IBM Power ISA 2.07 has been published on power.org, and IBM's new POWER8
processor is under development to implement that ISA. This patch provides
initial runtime and testsuite support for running Valgrind on POWER8 systems
running a soon-to-be released Linux distribution. This Linux distro will
include a POWER8-tuned libc that uses a subset of the new instructions from
ISA 2.07.  Since virtually all applications link with libc, it would be
impossible to run an application under Valgrind on this distro without adding
support for these new instructions to Valgrind, so that's the intent of this
patch. Note that applications built on this distro will *not* employ new POWER8
instructions by default. There are roughly 150 new instructions in the Power
ISA 2.07, including hardware transaction management (HTM). Support for these
new instructions (modulo the subset included in this bug) will be added to
Valgrind in a phased approach, similar to what we did for Power ISA 2.06.

Bugzilla 322294, VEX commit 2740

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13494 a5019735-40e9-0310-863c-91ae7b9d1cf9