[clang] [libcxx] [Clang] Implement CWG2369 "Ordering between constraints and substitution" (PR #102857)

[via cfe-commits]

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@@ -3876,6 +3864,41 @@ TemplateDeductionResult Sema::FinishTemplateArgumentDeduction(
     FD = const_cast<FunctionDecl *>(FDFriend);
     Owner = FD->getLexicalDeclContext();
   }
+
+  // C++20 [temp.deduct.general]p5: [DR2369]
----------------
cor3ntin wrote:

```suggestion
  // C++20 [temp.deduct.general]p5 (CWG2369):
```

https://github.com/llvm/llvm-project/pull/102857