Debug info tried to be emitted for unreachable code

[Aatch]

This code causes an ICE:

fn main() {
    println!("x");
    return;
    let test = if x() { 1 } else { 2 };
}

fn x() -> bool { unreachable!() }

complaining that the the test variable isn't an alloca. This is true, since we don't output any LLVM IR for unreachable code, which is everything after the return. For some reason, this only happens with if expressions (or at least, it doesn't happen with plain expressions or ordinary blocks) on the RHS.

[michaelwoerister]

Thanks for the report. Closing as duplicate of #21559.