[clang] [Clang] disallow non-lvalue values in constant expressions to prevent invalid pointer offset computation (PR #95479)

[via cfe-commits]

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@@ -858,6 +858,8 @@ Bug Fixes to C++ Support
 - Fixed several bugs in capturing variables within unevaluated contexts. (#GH63845), (#GH67260), (#GH69307),
   (#GH88081), (#GH89496), (#GH90669) and (#GH91633).
 - Fixed handling of brace ellison when building deduction guides. (#GH64625), (#GH83368).
+- Fixed a failed assertion when attempting to convert an integer representing the difference
+  between the addresses of two labels (a GNU extension) to a pointer within a constant expression. (GH95366).
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Sirraide wrote:

```suggestion
  between the addresses of two labels (a GNU extension) to a pointer within a constant expression. (#GH95366).
```

https://github.com/llvm/llvm-project/pull/95479