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

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> I did think about it more, and I think it would be more consistent to support the attribute on any sort of specializable entity, including functions - regardless of STL needs @AaronBallman @ldionne

Agreed; if we're adding a custom attribute, we might as well support it in a general form so users can also make use of it for their needs (which may be different than STL needs).

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