[clang] [APINotes] Add support for SWIFT_RETURED_AS_UNRETAINED_BY_DEFAULT (PR #138699)

[Saleem Abdulrasool via cfe-commits]

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@@ -624,6 +624,13 @@ class TagTableInfo
                                         ReleaseOpLength - 1);
       Data += ReleaseOpLength - 1;
     }
+    unsigned DefaultOwnershipLength =
+        endian::readNext<uint16_t, llvm::endianness::little>(Data);
+    if (DefaultOwnershipLength > 0) {
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compnerd wrote:

```suggestion
    if (unsigned DefaultOwnershipLength =
            endian::readNext<uint16_t, llvm::endianness::little>(Data)) {
```

This matches the style in the rest of the code.

https://github.com/llvm/llvm-project/pull/138699