Ability to use linkme in proc macros without requiring explicit dependency

[nazar-pc]

I have a procedural macro that outputs code with linkme, the problem is that it requires users of the macro to know about this and add linkme to explicit dependencies.

I'm wondering if it would be possible to add support for custom linkme path (rather than ::linkme) so I can customize it to point to re-exports.

Something like this:

#[distributed_slice(BENCHMARKS, linkme = "::other_crate::__private::linkme")]

This would be a big UX improvement for users of my crate.