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

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

How about taking a step at a time with this patch. Perhaps we should introduce the on-disk hash table infrastructure and always deserialize everything. Then we can verify that part works on our build infrastructure and then move on with the deferring the template loading. I believe that should be relatively easy to achieve with the current version of the patch.

Essentially I am proposing making `-fno-load-external-specializations-lazily` default so that we can test it without having to modify build infrastructure...

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