[clang] [C2y] Add octal prefixes, deprecate unprefixed octals (PR #131626)

[Aaron Ballman via cfe-commits]

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@@ -582,6 +582,12 @@ class Lexer : public PreprocessorLexer {
   /// sequence.
   static bool isNewLineEscaped(const char *BufferStart, const char *Str);
 
+  /// Diagnose use of a delimited or named escape sequence.
+  static void DiagnoseDelimitedOrNamedEscapeSequence(SourceLocation Loc,
+                                                     bool Named,
+                                                     const LangOptions &Opts,
+                                                     DiagnosticsEngine &Diags);
+
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AaronBallman wrote:

It's called from LiteralSupport.cpp, so it could be a non-member function, but I think it's a bit cleaner to scope it to the `Lexer` to make it clear this is emitting lexer-based diagnostics. WDYT?

https://github.com/llvm/llvm-project/pull/131626