[DAGCombiner] Optimize 1-bit smulo to AND+SETNE.

A 1-bit smulo overflows is both inputs are -1 since the result
should be +1 which can't be represented in a signed 1 bit value.

We can detect this with an AND and a setcc. The multiply result
can also use the same AND.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D97634