Test for other "unsafe attributes"

[workingjubilee]

Some attributes are implicitly unsafe, without containing the unsafe token in Rust. I will refer to these as "unsafe attributes". We probably need to replicate the work in #128 to make sure we detect these.

• Create tests for successfully denying all "unsafe attributes"
  • #[no_mangle] Catch #[no_mangle] #128
  • #[link_section] Catch #[no_mangle] #128
  • #[export_name] Test #[export_name] is blocked #177
  • #[link] maybe?
• Make all unsafe attribute tests pass
  • #[no_mangle] Catch #[no_mangle] #128
  • #[link_section] Turn us into a workspace #131
  • #[export_name] Test #[export_name] is blocked #177
  • #[link] maybe?

[thomcc]

#[link] is definitely something we need to forbid, but thankfully plrustc's lint against extern blocks does so. Closing as completed.