[clang] [clang] fix unresolved dependent template specialization mangling (PR #136201)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

I'm unfortunately quite a bit behind here in general, so I can't answer whether this is the RIGHT fix, but I definitely see that there isn't really anything questionable about the fix.  Sorry I can't be more helpful on that part, but I am at least OK with this to see if it fixes everyone's problems.

https://github.com/llvm/llvm-project/pull/136201