BranchProbabilityInfo - fix uninitialized variable warning. NFCI.

Author: RKSimon

llvm/include/llvm/Analysis/BranchProbabilityInfo.h

@@ -179,7 +179,7 @@ class BranchProbabilityInfo {
   DenseMap<Edge, BranchProbability> Probs;
 
   /// Track the last function we run over for printing.
-  const Function *LastF;
+  const Function *LastF = nullptr;
 
   /// Track the set of blocks directly succeeded by a returning block.
   SmallPtrSet<const BasicBlock *, 16> PostDominatedByUnreachable;