[clang] [llvm] [LLVM][Support] Enforce proper instantiations of `Registry<T>` (PR #185141)

[Balázs Benics via cfe-commits]

https://github.com/steakhal commented:

Thank you for thinking about this problem.
I like the symmetry proposed here with these macros.

https://github.com/llvm/llvm-project/pull/185141