[clang] [LifetimeSafety] Enable C support by default under -Wlifetime-safety (PR #224028)

[Benedek Kaibas via cfe-commits]

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@@ -379,6 +379,9 @@ features cannot lower the translation-unit ABI level;
   };
   ```
 
+- Lifetime safety analysis is now enabled for C by default. The `-fexperimental-lifetime-safety-c`
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benedekaibas wrote:

I think @Xazax-hun and @usx95 can make this call. I am fine doing the change. Just a side note: `-fexperimental-lifetime-safety-c` was not included in the lifetime safety documentation, so I do not expect many uses cases of it except the teams that were already aware of it.

https://github.com/llvm/llvm-project/pull/224028