Select expensive add/sub/cmp interpretations for blocks containing
Iop_GetMSBs8x16, since the presence of those usually implies PMOVMSKB
instructions in the block, which can mean "inlined string operations".
Reduces the noise level a lot in some icc12 -O2 generated sequences.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13757 a5019735-40e9-0310-863c-91ae7b9d1cf9