[clang] [Clang] Ignore -fchar8_t in C (PR #138716)

[Aaron Ballman via cfe-commits]

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@@ -317,6 +317,8 @@ Modified Compiler Flags
 
 - The ``-mexecute-only`` and ``-mpure-code`` flags are now accepted for AArch64 targets. (#GH125688)
 
+- The ``-fchar8_t`` flag is no longer consider in non-C++ languages modes. (#GH55373)
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AaronBallman wrote:

```suggestion
- The ``-fchar8_t`` flag is now diagnosed in non-C++ languages modes. (#GH55373)
```

https://github.com/llvm/llvm-project/pull/138716