Do not legalize large add with addc/adde, introduce addcarry and do it with uaddo...

Do not legalize large add with addc/adde, introduce addcarry and do it with uaddo/addcarry

Summary: As per discution on how to get better codegen an large int legalization, it became clear that using a glue for the carry was preventing several desirable optimizations. Passing the carry down as a value allow for more flexibility.

Reviewers: jyknight, nemanjai, mkuper, spatel, RKSimon, zvi, bkramer

Subscribers: igorb, llvm-commits

Differential Revision: https://reviews.llvm.org/D29872

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301775 91177308-0d34-0410-b5e6-96231b3b80d8