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

[Ramkumar Ramachandra via llvm-commits]

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@@ -226,6 +226,12 @@ class DenseMapBase : public DebugEpochBase {
     return Default;
   }
 
+  ValueT lookup_or(const_arg_type_t<KeyT> Val, const ValueT &Default) const {
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artagnon wrote:

Thanks a lot! I didn't think to use Compiler Explorer. I've now updated the patch and commit message.

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