[clang] [Clang][C++26] Implement Pack Indexing (P2662R3). (PR #72644)

[Louis Dionne via cfe-commits]

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@@ -978,6 +978,20 @@ bool Parser::ConsumeAndStoreFunctionPrologue(CachedTokens &Toks) {
       } else {
         break;
       }
+      // Pack indexing
+      if (getLangOpts().CPlusPlus26 && Tok.is(tok::ellipsis) &&
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ldionne wrote:

I think it might be possible to maintain the same ABI we have right now while changing how it's implemented, yes. It probably requires a bit of thought but it's probably possible. But there's certainly no point in any of this if GCC doesn't add this extension, from my point of view at least.

https://github.com/llvm/llvm-project/pull/72644