[clang] [clang] fix merging of UsingShadowDecl (PR #80245)

[Matheus Izvekov via cfe-commits]

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@@ -181,6 +181,9 @@ Bug Fixes to C++ Support
   and (`#79745 <https://github.com/llvm/llvm-project/issues/79745>`_)
 - Fix incorrect code generation caused by the object argument of ``static operator()`` and ``static operator[]`` calls not being evaluated.
   Fixes (`#67976 <https://github.com/llvm/llvm-project/issues/67976>`_)
+- Fix incorrect merging of modules which contain using declarations which shadow
+  other declarations. This could manifest as ODR checker false positives.
+  Fixes (`#TODO <https://github.com/llvm/llvm-project/issues/TODO>`_)
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mizvekov wrote:

The MR is split in two commits, the first one adds the test, if you click on the last commit, you can see the change in the expectation.

https://github.com/llvm/llvm-project/pull/80245