Unweaken vtables as per http://llvm.org/docs/CodingStandards.html#ll_virtual_anch

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146960 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Metadata.h

@@ -36,6 +36,7 @@ template<typename ValueSubClass, typename ItemParentClass>
 /// These are used to efficiently contain a byte sequence for metadata.
 /// MDString is always unnamed.
 class MDString : public Value {
+  virtual void anchor();
   MDString(const MDString &);            // DO NOT IMPLEMENT
 
   StringRef Str;