[TargetLowering][DAGCombine][MSP430] Shift Amount Threshold in DAGCombine (3) (baseline tests)

Summary:
This is baseline tests for D69326

Incorporates a command line flag for the MSP430 and adds a test cases to help showing the effects of applying D69326

More details and motivation for this patch in D69326

Reviewers: spatel, asl, lebedev.ri

Reviewed By: spatel, asl

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69975