[clang] [Serialization] Handle uninitialized type constraints (PR #110496)

[Florian Albrechtskirchinger via cfe-commits]

falbrechtskirchinger wrote:

> Bump, it would be nice to have this or that fix backported to 19.x

@vient Backport is happening. #113182

https://github.com/llvm/llvm-project/pull/110496