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

[Richard Smith via llvm-commits]

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@@ -7245,6 +7245,11 @@ let Visibility = [CC1Option, CC1AsOption, FC1Option] in {
 def tune_cpu : Separate<["-"], "tune-cpu">,
   HelpText<"Tune for a specific cpu type">,
   MarshallingInfoString<TargetOpts<"TuneCPU">>;
+def fexec_charset : Separate<["-"], "fexec-charset">, MetaVarName<"<charset>">,
+  HelpText<"Set the execution <charset> for string and character literals. "
+           "Supported character encodings include ISO8859-1, UTF-8, IBM-1047 "
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zygoloid wrote:

I think this is too long for `HelpText`, which is displayed by `clang --help`. Also, aren't `ISO8859-1`, `UTF-8`, and `IBM-1047` all covered by "those supported by the host icu or iconv library"? Do we really need to call them out separately?

Maybe something like "Use <charset> for string and character literals" could work here as help text? You can put longer information with examples of character set names and references to icu / iconv into a separate `DocBrief` argument.

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