[clang] [Clang][Sema] Fix crash when MS dependent base class lookup occurs in an incomplete context (PR #83024)

[Erich Keane via cfe-commits]

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@@ -283,6 +283,7 @@ Bug Fixes to C++ Support
   (`#78524 <https://github.com/llvm/llvm-project/issues/78524>`_)
 - Clang no longer instantiates the exception specification of discarded candidate function
   templates when determining the primary template of an explicit specialization.
+- Fixed a crash when MS unqualified dependent base class lookup occurs in an incomplete class.
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erichkeane wrote:

```suggestion
- Fixed a crash in Microsoft compatibility  mode where unqualified dependent base class lookup occurs on an incomplete class.
```

https://github.com/llvm/llvm-project/pull/83024