[DenseMap] Use std::remove_cv_t

Author: artagnon

llvm/include/llvm/ADT/DenseMap.h

@@ -220,13 +220,8 @@ class DenseMapBase : public DebugEpochBase {
   // Return the entry with the specified key, or \p Default. This variant is
   // useful, because `lookup` cannot be used with non-default-constructible
   // values.
-  ValueT lookup_or(const_arg_type_t<KeyT> Val, ValueT &&Default) const {
-    if (const BucketT *Bucket = doFind(Val))
-      return Bucket->getSecond();
-    return Default;
-  }
-
-  ValueT lookup_or(const_arg_type_t<KeyT> Val, const ValueT &Default) const {
+  template <typename U = std::remove_cv_t<ValueT>>
+  ValueT lookup_or(const_arg_type_t<KeyT> Val, U &&Default) const {
     if (const BucketT *Bucket = doFind(Val))
       return Bucket->getSecond();
     return Default;