[SelectionDAG] Fix constant offset folding to avoid commuting non-commutative operators.

This fixes a miscompile in MultiSource/Benchmarks/MiBench/consumer-lame
introduced in r258296.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258366 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed