Plog a memleak in GlobalOpt.

Found by valgrind.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151525 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index acb723e..58ab567 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2559,7 +2559,7 @@
         ValueStack.push_back(new DenseMap<Value*, Constant*>);
         if (!EvaluateFunction(Callee, RetVal, Formals))
           return false;
-        ValueStack.pop_back();
+        delete ValueStack.pop_back_val();
         InstResult = RetVal;
 
         if (InvokeInst *II = dyn_cast<InvokeInst>(CurInst)) {