[clang] Add C language support for clang-format IntegerLiteralSeparator (PR #182296)

[John Mitchell via cfe-commits]

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@@ -4751,8 +4751,8 @@ the configuration (without a prefix: ``Auto``).
 .. _IntegerLiteralSeparator:
 
 **IntegerLiteralSeparator** (``IntegerLiteralSeparatorStyle``) :versionbadge:`clang-format 16` :ref:`¶ <IntegerLiteralSeparator>`
-  Format integer literal separators (``'`` for C++ and ``_`` for C#, Java,
-  and JavaScript).
+  Format integer literal separators (``'`` for C, C++ and ``_`` for C#, Java,
+  and JavaScript).  Note that using the separator with C requires a C23+ compiler.
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fauxprogrammer wrote:

Ah, didn't realize that, thank you!  Do I still include the .rst file in the changeset? 

https://github.com/llvm/llvm-project/pull/182296