Correctly report Changed status in FoldBranchToCommonDest

[serge-sans-paille]

Summary

It's possible for the first loop trip to set the Changed Status, and to another
one to early exit, so take that into account.

[foad]

Seems obviously correct.

llvm/lib/Transforms/Utils/SimplifyCFG.cpp

if (BasicBlock *PB = BB->getSinglePredecessor())
                I != E;) {
             Instruction *Curr = &*I++;
             if (isa<CmpInst>(Curr)) {
               Cond = Curr;
               break;
             }
             // Quit if we can't remove this instruction.
             if (!tryCSEWithPredecessor(Curr, PB))
-              return false;
+              return Changed;
             Changed = true;
           }
         }
 
     if (!Cond)
       return Changed;
   }