[BranchFolding] Fix live-in's when hoisting code

Summary:
When the branch folder hoist code into a predecessor it adjust live-in's
in the blocks it hoist code from. However it fail to handle hoisted code
that contain a defed register that originally is live-in in the block
through a super register.

This is fixed by replacing the live-in handling code with calls to
utility functions in LivePhysRegs.

Reviewers: kparzysz, gberry, MatzeB, uweigand, aprantl

Reviewed By: kparzysz

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D47529

llvm-svn: 334163