[SimplifyCFG] Fix for non-determinism in codegen

[mgrang]

Summary

This patch fixes issues in codegen uncovered due to https://reviews.llvm.org/D26703

[mgrang]

Will resubmit this and add llvm-commits as subscriber.

lib/Transforms/Utils/SimplifyCFG.cpp

bool SimplifyCFGOpt::SimplifyCommonResume(ResumeInst *RI) {
   // Check that there are no other instructions except for debug intrinsics
   // between the phi of landing pads (RI->getValue()) and resume instruction.
   BasicBlock::iterator I = cast<Instruction>(RI->getValue())->getIterator(),
                        E = RI->getIterator();
   while (++I != E)
     if (!isa<DbgInfoIntrinsic>(I))
       return false;
 
-  SmallSet<BasicBlock *, 4> TrivialUnwindBlocks;
+  SmallSetVector<BasicBlock *, 4> TrivialUnwindBlocks;
   auto *PhiLPInst = cast<PHINode>(RI->getValue());
 
   // Check incoming blocks to see if any of them are trivial.
   for (unsigned Idx = 0, End = PhiLPInst->getNumIncomingValues(); Idx != End;
        Idx++) {
     auto *IncomingBB = PhiLPInst->getIncomingBlock(Idx);
     auto *IncomingValue = PhiLPInst->getIncomingValue(Idx);