[clang] [Serialization] Fix lazy template loading (PR #133057)

[Jonas Hahnfeld via cfe-commits]

hahnjo wrote:

Ok, this wasn't too bad actually: https://github.com/llvm/llvm-project/pull/170090 fixes the reproducer, so fingers crossed it also addresses the issue in the full-blown internal code :crossed_fingers: @alexfh if you have more cycles available, could you test the two PRs together?

https://github.com/llvm/llvm-project/pull/133057