[clang] [NFC][doc] Mark P1857R3 as partial implemented (PR #164095)

[via cfe-commits]

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@@ -926,7 +926,14 @@ <h2 id="cxx20">C++20 implementation status</h2>
       </tr>
       <tr>
         <td><a href="https://wg21.link/p1857r3">P1857R3</a></td>
-        <td class="none" align="center">No</td>
+        <td class="partial" align="center">
+          <details>
+            <summary>>Clang 21(Partial)</summary>
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h-vetinari wrote:

```suggestion
            <summary>Clang 21 (Partial)</summary>
```

https://github.com/llvm/llvm-project/pull/164095