Writing a New Operator

Howdy yall, October again

After a little bit of digging, I've come to the conclusion that I have no
idea how consteval functions are handled in gcc, and even less so how I'd
go about using one as an operator, as would be required for compile-time
verification of an annotation target.

The largest issue on that front is simply the fact that I need to be able
to call the operator function (which I do not know how to get or use) with
the correct parameters (of which I believe I know what I'd have to do, but
the how of it is currently beyond me) at the right time (which I am also
currently unsure of how to do).

Creating an implicitly defined operator for it is something I *think* I've
solved, at the very least I'm pretty sure I've solved the generation of the
function signature that would end up in `implicitly_declared_fn` but that
doesn't solve the rest of the issues I'd be running into with
implementation, namely retrieving and using said operator as stated above.

I believe most of the direction I require in this specific case is a
general area to start researching to begin to understand what working with
consteval functions requires as well as how to check that a function is
declared as such, as I'm fairly certain that `DECL_DECLARED_CONSTEXPR_P` is
not what I want in that regard based on the documentation and usages.