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

[Vassil Vassilev via cfe-commits]

vgvassilev 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...

In that case we need to understand how this patch differs from the one I pasted in phabricator since the one there works for that case I assume. 

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