[x86] Propagate memory operands during ISel DAG postprocessing

Summary:
Propagate memory operands when folding test instructions.

This was split from D80062.

Reviewers: craig.topper, rnk, lebedev.ri

Reviewed By: craig.topper

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80140