x86: Add string/memory function tests in RTM region

At function exit, AVX optimized string/memory functions have VZEROUPPER
which triggers RTM abort.   When such functions are called inside a
transactionally executing RTM region, RTM abort causes severe performance
degradation.  Add tests to verify that string/memory functions won't
cause RTM abort in RTM region.

(cherry picked from commit 4bd660be)