[clang] [clang] Stub out gcc_struct attribute (PR #71148)

[Aaron Ballman via cfe-commits]

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@@ -7482,3 +7482,26 @@ generation of the other destruction cases, optimizing the above `foo.destroy` to
 
   }];
 }
+
+def MSStructDocs : Documentation {
+  let Category = DocCatDecl;
+  let Content = [{
+The ``ms_struct`` and ``gcc_struct`` attributes request the compiler to enter a
+special record layout compatibility mode which mimics the layout of Microsoft or
+Itanium C++ ABI respectively. Obviously, if the current C++ ABI matches the
+requested ABI, the attribute does nothing. However, if it does not, annotated
+structure or class is laid out in a special compatibility mode, which slightly
+changes offsets for fields and bit-fields. The intention is to match the layout
+of the requested ABI for structures which only use C features.
+
+Note that the default behavior can be controlled by ``-mms-bitfields`` and
+``-mno-ms-bitfields`` switches and via ``#pragma ms_struct``.
+  }];
+}
+
+def GCCStructDocs : Documentation {
+  let Category = DocCatDecl;
+  let Content = [{
+See ms_struct_.
+  }];
+}
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AaronBallman wrote:

```suggestion

```

https://github.com/llvm/llvm-project/pull/71148