'grail' fixes for s390x:
This isn't a good result. It merely disables the new functionality on s390x,
for the reason stated below.
* guest_generic_bb_to_IR.c bb_to_IR(): Disable, hopefully temporarily, the key
&&-recovery transformation on s390x, since it causes Memcheck to crash for
reasons I couldn't figure out. It also exposes some missing Iex_ITE cases
in the s390x insn selector, although those shouldn't be a big deal to fix.
Maybe it's some strangeness to do with the s390x "ex" instruction. I don't
exactly understand how that trickery works, but from some study of it, I
didn't see anything obviously wrong.
It is only chasing through conditional branches that is disabled for s390x.
Chasing through unconditional branches (jumps and calls to known
destinations) is still enabled.
* host_s390_isel.c s390_isel_cc(): No functional change. Code has been added
here to handle the new Iop_And1 and Iop_Or1, and it is somewhat tested, but
is not needed until conditional branch chasing is enabled on s390x.