`unsafe` blocks do not fire `unsafe_code` lint

[ehuss]

RFC 3484 indicated that an unsafe block should fire the unsafe_code lint. However, it does not appear to do that, yet.

#![feature(unsafe_extern_blocks)]
#![warn(unsafe_code)]

unsafe extern "C" {
    pub fn foo();
}

Expected results: Should fire the unsafe_code lint.

Actual results: Lint is not fired.

Meta

rustc 1.81.0-nightly (59e2c01c2 2024-06-17)
binary: rustc
commit-hash: 59e2c01c2217a01546222e4d9ff4e6695ee8a1db
commit-date: 2024-06-17
host: aarch64-apple-darwin
release: 1.81.0-nightly
LLVM version: 18.1.7

cc @spastorino FYI, I didn't see a discussion of further work needing to be done in #124482, so I wanted to make sure it gets tracked.

Tracking:

• Tracking Issue for RFC 3484: Unsafe Extern Blocks #123743