[llvm] [DenseMap] Fix MSVC buildbot failure in lookup_or (PR #142268)

[Jakub Kuderski via llvm-commits]

================
@@ -220,7 +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 {
+  template <typename U = std::remove_cv_t<ValueT>>
----------------
kuhar wrote:

Oh I apologize -- it only affects the type for `Default`. I misread the code.

https://github.com/llvm/llvm-project/pull/142268