On a zEC12 or z13, a glibc with lock elision enabled infers from HWCAP

On a zEC12 or z13, a glibc with lock elision enabled infers from HWCAP
that the prerequisites for lock elision are met.  Then it may use TBEGIN
and other transactional-execution instructions which are not implemented
by Valgrind.  Likewise, the upcoming glibc 2.23 will exploit vector
instructions if they are advertised by HWCAP; and those are currently
not implemented by Valgrind either.  In general, the increased use of
ifunc may lead to more such cases in the future.

This patch suppresses the advertising of those hardware features via
HWCAP which are either not known to Valgrind or currently unsupported.

Patch by Andreas Arnez (arnez@linux.vnet.ibm.com).
Fixes BZ #353680.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@15702