[clang] [clang] Fix high memory consumption during pack deduction (PR #88637)

[Erich Keane via cfe-commits]

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@@ -831,7 +831,7 @@ class PackDeductionScope {
     if (IsPartiallyExpanded)
       PackElements += NumPartialPackArgs;
     else if (IsExpanded)
-      PackElements += *FixedNumExpansions;
+      PackElements += FixedNumExpansions.value_or(1);
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erichkeane wrote:

I don't have a great idea here either.  It seems to me that we shouldnt get here without a pack, and the bug is sooner, but I dont have a great idea of where we should be catching that case.

https://github.com/llvm/llvm-project/pull/88637