[clang] [clang][NFC] Refactor Builtins.def to be a tablegen file (PR #68324)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,333 @@
+//=- ClangDiagnosticsEmitter.cpp - Generate Clang diagnostics tables -*- C++ -*-
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// These tablegen backends emit Clang diagnostics tables.
----------------
AaronBallman wrote:

```suggestion
// This tablegen backend emits Clang's builtins tables.
```

https://github.com/llvm/llvm-project/pull/68324