[SystemZ] Handle SADDO et.al. and ADD/SUBCARRY

[SystemZ] Handle SADDO et.al. and ADD/SUBCARRY

This provides an optimized implementation of SADDO/SSUBO/UADDO/USUBO
as well as ADDCARRY/SUBCARRY on top of the new CC implementation.

In particular, multi-word arithmetic now uses UADDO/ADDCARRY instead
of the old ADDC/ADDE logic, which means we no longer need to use
"glue" links for those instructions.  This also allows making full
use of the memory-based instructions like ALSI, which couldn't be
recognized due to limitations in the DAG matcher previously.

Also, the llvm.sadd.with.overflow et.al. intrinsincs now expand to
directly using the ADD instructions and checking for a CC 3 result.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331203 91177308-0d34-0410-b5e6-96231b3b80d8