Recommit r360171: [DAGCombiner] Avoid creating large tokenfactors in visitTokenFactor.

If we hit the limit, we do expand the outstanding tokenfactors.
Otherwise, we might drop nodes with users in the unexpanded
tokenfactors. This fixes the crashes reported by Jordan Rupprecht.

Reviewers: niravd, spatel, craig.topper, rupprecht

Reviewed By: niravd

Differential Revision: https://reviews.llvm.org/D62633

llvm-svn: 362350