Do early writeback of the base register for the following instruction
forms, to stop Memcheck complaining about writes below the stack
pointer:
  str x3, [sp,#-16]!
  stp q0, q1, [sp,#-512]!



git-svn-id: svn://svn.valgrind.org/vex/trunk@2835 8f6e269a-dfd6-0310-a8e1-e2731360e62c
Implement a couple of backend artefacts needed by Memcheck on large
applications:
  Iop_CmpNEZ64x2 expressions
  Ijk_NoRedir block terminators


git-svn-id: svn://svn.valgrind.org/vex/trunk@2836 8f6e269a-dfd6-0310-a8e1-e2731360e62c