able to invoke unstable macro 2.0

[durka]

Stability checking for macro_rules! was fixed in #48524, but uses of declarative macros 2.0 (macro items) are still not checked for stability.

ORIGINAL ISSUE:

Why does this compile?

fn main() {
    __thread_local_inner!(i32, 42);
}

__thread_local_inner is marked #[unstable(...)] #[allow_internal_unstable].

[petrochenkov]

Because macros are not checked for stability!
At least this was the case when I made stability annotations on public macros mandatory in hopes of a better future.

[jseyfried]

cc me

[abonander]

I'm looking into implementing this, however are we just looking at macro_rules! macros for now or proc-macro and syntax extension invocations as well?

cc @nrc

[petrochenkov]

@abonander
I'm reopening this because macros 2.0 (macro items) are not checked for stability yet.