[DAG] SimplifyDemandedBits - Use DemandedBits intead of OriginalDemandedBits...

[DAG] SimplifyDemandedBits - Use DemandedBits intead of OriginalDemandedBits to when simplifying UMIN/UMAX to AND/OR.

DemandedBits is forced to all ones if there are multiple users.

The changes X86 test cases looks like they were miscompiles before.
The value of eax/rax from the cmov is returned from the function in
addition to being used by the sar. That usage needs all bits even
though the sar doesn't.