[Rust 2018] Inconsistent anonymous lifetimes

[CryZe]

This is allowed by Rust 2018:

impl<T: SomeTrait<'_>> SomeType<T> { ... }

while this is not allowed:

fn foo<T: SomeTrait<'_>>() { ... }

[CryZe]

I replicated this on the playground: https://play.rust-lang.org/?gist=b7f75c8e5df6945c2065892882b59764&version=nightly&mode=debug&edition=2018

[aturon]

Duplicate of #45667