[clang] [win][clang] Align scalar deleting destructors with MSABI (PR #139566)

[via cfe-commits]

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@@ -34,6 +34,24 @@ latest release, please see the `Clang Web Site <https://clang.llvm.org>`_ or the
 Potentially Breaking Changes
 ============================
 
+- Scalar deleting destructor support has been aligned with MSVC when
+  targeting the MSVC ABI. Clang previously implemented support for
+  ``::delete`` by calling the complete object destructor and then the
+  appropriate global delete operator (as is done for the Itanium ABI).
+  The scalar deleting destructor is now called to destroy the object
+  and deallocate its storage. This is an ABI change that can result in
+  memory corruption when a program built for the MSVC ABI has
+  portions compiled with clang 21 or earlier and portions compiled
+  with a version of clang 22 (or MSVC). Consider a class ``X`` that
+  declares a virtual destructor and an ``operator delete`` member
+  with the destructor defined in library ``A`` and a call to `::delete`` in
+  library ``B``. If library ``A`` is compiled with clang 21 and library ``B``
+  is compiled with clang 22, the ``::delete`` call might dispatch to the
+  scalar deleting destructor emitted in library ``A`` which will erroneously
+  call the member ``operator delete`` instead of the expected global
+  delete operator. The old behavior is retained under ``-fclang-abi-compat=20``
----------------
h-vetinari wrote:

This looks like a left-over
```suggestion
  delete operator. The old behavior is retained under ``-fclang-abi-compat=21``
```

https://github.com/llvm/llvm-project/pull/139566