able to invoke unstable macro 2.0

Stability checking for `macro_rules!` was fixed in https://github.com/rust-lang/rust/pull/48524, but uses of declarative macros 2.0 (`macro` items) are still not checked for stability.

#### ORIGINAL ISSUE:

Why does this compile?

``` rust
fn main() {
    __thread_local_inner!(i32, 42);
}
```

`__thread_local_inner` is marked `#[unstable(...)] #[allow_internal_unstable]`.
