[clang] [clang][MSVC] Correct mangling of thread-safe static initialization variables. (PR #85300)

[David Majnemer via cfe-commits]

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@@ -47,6 +47,12 @@ C++ Specific Potentially Breaking Changes
 
 ABI Changes in This Version
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+- Fixed Microsoft name mangling of implicitly defined variables used for thread
+  safe static initialization of static local variables. This change resolves
+  incompatibilities with code compiled by MSVC but might introduce
+  incompatibilities with code compiled by earlier versions of Clang when an
+  inline member function that contains a static local variable with a dynamic
+  initializer is declared with ``__declspec(dllimport)``. (#GH83616).
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majnemer wrote:

The only thing we try to do is respect the version of MSVC we are attempting to be compatible with.

https://github.com/llvm/llvm-project/pull/85300