[clang] [clang] Add __nullptr as a keyword to C (PR #123119)

[Aaron Ballman via cfe-commits]

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@@ -514,9 +514,7 @@ available in all language modes.
 __nullptr
 ---------
 
-``__nullptr`` is an alternate spelling for ``nullptr``, but is also available in
-C++ modes prior to C++11. Note that it's currently not availbale in C despite
-C23 having support for ``nullptr``.
+``__nullptr`` is an alternate spelling for ``nullptr``, it is available since C++98 and C23.
----------------
AaronBallman wrote:

```suggestion
``__nullptr`` is an alternate spelling for ``nullptr``. It is available in all C and C++ language modes.
```

https://github.com/llvm/llvm-project/pull/123119