[clang] [llvm] Enable fexec-charset option (PR #138895)

[Sergei Barannikov via cfe-commits]

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@@ -135,6 +135,9 @@ class TextEncodingConverter {
       return std::string(Result);
     return EC;
   }
+
+  // Maps the encoding name to enum constant if possible.
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s-barannikov wrote:

This looks like exposing an implementation detail. Should we instead add a method checking if the conversion is supported?

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The comment should be doxygen-style (///).

https://github.com/llvm/llvm-project/pull/138895