Destroy ValueNames after all unique_ptr<Value>

This UB detected by -fsanitize-memory-use-after-dtor in tensorflow/MLIR.

llvm/lib/IR/LLVMContextImpl.h

@@ -1386,6 +1386,8 @@ class LLVMContextImpl {
   LLVMContext::YieldCallbackTy YieldCallback = nullptr;
   void *YieldOpaqueHandle = nullptr;
 
+  DenseMap<const Value *, ValueName *> ValueNames;
+
   using IntMapTy =
       DenseMap<APInt, std::unique_ptr<ConstantInt>, DenseMapAPIntKeyInfo>;
   IntMapTy IntConstants;
@@ -1402,8 +1404,6 @@ class LLVMContextImpl {
   DenseMap<Value *, ValueAsMetadata *> ValuesAsMetadata;
   DenseMap<Metadata *, MetadataAsValue *> MetadataAsValues;
 
-  DenseMap<const Value *, ValueName *> ValueNames;
-
 #define HANDLE_MDNODE_LEAF_UNIQUABLE(CLASS)                                    \
   DenseSet<CLASS *, CLASS##Info> CLASS##s;
 #include "llvm/IR/Metadata.def"