Compiler keeps running after it emits a compilation error

[DutchGhost]

The following code does not compile, however the compiler keeps running after emitting a message it could not compile:
https://play.rust-lang.org/?gist=7dc801439d22e1d11c9025092d757099&version=stable&mode=debug

const q: () = 'a: while (continue 'a != break 'a) {};

fn main() {
    let q: ();
}

The error is:

|                                         ^^^^^^^^
  |
  = note: #[warn(unreachable_code)] on by default

error[E0019]: constant contains unimplemented expression type
 --> src/main.rs:1:26
  |
1 | const q: () = 'a: while (continue 'a != break 'a) {};
  |                          ^^^^^^^^^^^

warning: Constant evaluating a complex constant, this might take some time
 --> src/main.rs:1:1
  |
1 | const q: () = 'a: while (continue 'a != break 'a) {};
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

when let q: (); is removed, it just fails to compile, and rustc stops running.

[betawaffle]

Duplicate of #50637