Memcheck on amd64; fix false positive associated with spec cases {Z,NZ} after {LOGICB...

Memcheck on amd64; fix false positive associated with spec cases {Z,NZ} after {LOGICB,LOGICW}.  n-i-bz.

For the spec cases {Z,NZ} after {LOGICB,LOGICW}, which are simply comparisons
of the result against zero, use Cmp{EQ,NE}32 rather than their 64-bit
counterparts.  This is because Memcheck on amd64 instruments the 32 bit
versions exactly, at the default --expensive-definedness-checks=auto setting.
The alternative would have been to make Memcheck also do exact instrumentation
of the 64 bit versions, but that would also burden all other 64 bit eq/ne
comparisons with that cost for no purpose.  So this is a cheaper solution.