Do not call SplitBlockPredecessors on a loop preheader when one of the
predecessors is an indirectbr. Otherwise, you will hit this assert:
!isa<IndirectBrInst>(Preds[i]->getTerminator()) && "Cannot split an edge from an IndirectBrInst"
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153134 91177308-0d34-0410-b5e6-96231b3b80d8
