[DAGcombine] Teach the combiner about -a = ~a + 1
Summary: This include variant for add, uaddo and addcarry. usubo and subcarry require the carry to be flipped to preserve semantic, but we chose to do the transform anyway in that case as to push the transform down the carry chain.
Reviewers: efriedma, spatel, RKSimon, zvi, bkramer
Differential Revision: https://reviews.llvm.org/D46505