Fix a problem with double freeing memory.  For some reason, CallGraph is not
acting like a normal pass.  :(


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@13318 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/IPA/CallGraph.cpp b/lib/Analysis/IPA/CallGraph.cpp
index 74a28d8..70bf2c4 100644
--- a/lib/Analysis/IPA/CallGraph.cpp
+++ b/lib/Analysis/IPA/CallGraph.cpp
@@ -126,6 +126,7 @@
     delete I->second;
   FunctionMap.clear();
   delete CallsExternalNode;
+  CallsExternalNode = 0;
 }
 
 static void WriteToOutput(const CallGraphNode *CGN, std::ostream &o) {