[clang] [clang] fix unresolved dependent template specialization mangling (PR #135111)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

> https://godbolt.org/z/sY44dG6Ya is the reproducer. It is not super small but still should give an idea as the stack is quite similar to stuff touched by this PR.

Did you open a bug report? Maybe w/ reduction is ends up the same as the one I just linked to.

https://github.com/llvm/llvm-project/pull/135111