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

[Mital Ashok via cfe-commits]

MitalAshok wrote:

A list of places this could be used:

https://eel.is/c++draft/cmp.result#1
https://eel.is/c++draft/meta.rqmts#4
https://eel.is/c++draft/execpol.type#3
https://eel.is/c++draft/format.arg#2
https://eel.is/c++draft/range.adaptor.object#5
https://eel.is/c++draft/coro.generator.class#4
https://eel.is/c++draft/time.traits.is.clock#2
https://eel.is/c++draft/saferecl.rcu.base#2
https://eel.is/c++draft/saferecl.hp.base#2

Also consider adding an argument that lets you diagnose https://eel.is/c++draft/namespace.std#2.1

>  - the added declaration depends on at least one program-defined type,

To diagnose specializations for `std::pair<int, int>`, but allow `std::pair<MyClass, int>`.

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