[clang] [Serialization] Load Specializations Lazily (PR #76774)

[Jonas Hahnfeld via cfe-commits]

hahnjo wrote:

I tried applying this patch to ROOT/Cling and it fails to build because something is of the opinion that `std::is_integral<int>::value` is not true. I don't have time right now to investigate further, but since this is the only change I did it is highly likely that it's caused by this...

https://github.com/llvm/llvm-project/pull/76774