[clang] [Clang] Add [[clang::no_specializations]] (PR #101469)

[via cfe-commits]

cor3ntin wrote:

Does it makes sense to also support function templates?
For example, my understanding is that specializing `is_pointer_interconvertible_with_class()` would be UB

https://github.com/llvm/llvm-project/pull/101469