`linkage` attribute can be applied to any item

[oli-obk]

I tried this code:

#![feature(linkage)]
#[linkage = "external"]
type Foo = ();

I expected to see this happen: compilation failure because of attribute on an item where it makes no sense

Instead, this happened: compiled successfully

Meta

rustc --version --verbose:

1.82.0-nightly

2024-07-31 28a58f2fa7f0c46b8fab

cc #29603

see #128444 for where to fix this issue

[s7tya]

@rustbot claim