[DAG] select Cond, C, -1 --> or (sext (not Cond)), C when C is MVT::i1

In the spirit of D130765 . Get rid of cbranches and/or cmov. Usually shorter, but sometime not, becaus eit's hard to prededict when dependency breaking xor will be introduced.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D134736