Add test cases for 128-bit shadow loads with --partial-loads-ok={yes,no}
in such a way that they can be shared across targets that support 128 bit
loads, as required.  amd64 only right now.  Adds memcheck/tests/common
to hold this stuff.  Bug #294285.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13491 a5019735-40e9-0310-863c-91ae7b9d1cf9