[msan] Fix a few compilation warnings.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168878 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Instrumentation/MemorySanitizer.cpp

@@ -186,8 +186,8 @@ private:
   /// \brief An empty volatile inline asm that prevents callback merge.
   InlineAsm *EmptyAsm;
 
-  friend class MemorySanitizerVisitor;
-  friend class VarArgAMD64Helper;
+  friend struct MemorySanitizerVisitor;
+  friend struct VarArgAMD64Helper;
 };
 }  // namespace
 
@@ -336,6 +336,8 @@ struct VarArgHelper {
   /// This method is called after visiting all interesting (see above)
   /// instructions in a function.
   virtual void finalizeInstrumentation() = 0;
+
+  virtual ~VarArgHelper() {}
 };
 
 struct MemorySanitizerVisitor;