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

[Erich Keane 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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erichkeane wrote:

Would a change like that be possible without being an ABI break?  I might bring @AaronBallman into this here discussion and see what we think here.  I see value in enabling it here and hoping GCC does someday, but not sure I'm in favor of it, unless this is something you could use ANYWAY without their support.

Another thing is perhaps we could ask @jicama what GCC intends to do here (or at least for his thoughts/see if we can influence them)?  @jwakely might have something to say as well.

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