Bug 502324 - s390x: Fix memcheck false positives with TMxx

Bug 502324 - s390x: Fix memcheck false positives with TMxx

The 16-bit "test under mask" instructions TMLL, TMLH, TMHL, and TMHH can
yield memcheck false positives when:

* some of the operand bits in the tested 16-bit chunk (but outside the
  mask) are undefined

* the resulting condition code is used in a different block

In this case the condition code is computed by the helper
s390_call_calculate_cond, with the full 16-bit chunk and the given mask as
arguments.  Since the 16-bit chunk is not fully defined, memcheck
complains.

To fix this, AND the operand with the given mask before storing it for use
as a helper argument.  Also, optimize the frequent case of testing a
single bit.  For this purpose, add S390_CC_OP_BITWISE2 as a new way of
computing the condition code.