[clang] clang: Relax LangOpts checks when lexing quoted numbers during preprocessing (PR #95798)

[Aaron Ballman via cfe-commits]

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@@ -2068,7 +2068,8 @@ bool Lexer::LexNumericConstant(Token &Result, const char *CurPtr) {
   }
 
   // If we have a digit separator, continue.
-  if (C == '\'' && (LangOpts.CPlusPlus14 || LangOpts.C23)) {
+  if (C == '\'' &&
+      (LangOpts.CPlusPlus14 || LangOpts.C23 || ParsingPreprocessorDirective)) {
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AaronBallman wrote:

> Sure, but we don't have to expose that language extension to users, it can remain internal to the compiler.

This still doesn't address my concerns from earlier about how it impacts maintenance of Clang itself:

> I don't think per-feature LangOptions is viable. There's digit separators, hex float support, binary literal support, different literal suffixes, various keywords, etc and that doesn't seem likely to scale well. Also, it makes it seem like we support a la carte language features when we don't -- we intentionally don't want to let users disable standard features (in general; exceptions exist) and so that approach gives the impression contributors need to check both language mode and feature availability which is a maintenance concern.

How do we avoid this situation, as that's my primary concern.

https://github.com/llvm/llvm-project/pull/95798