Incorrect codegen with shadowed constants in a match arm

[Aatch]

From @eefriedman's comment in #27033:

fn main() {
    const C: u8 = 3;
    match 1 {
        C @ 2 => { println!("{}", C); }
        _ => {}
    };
}

<anon>:4:9: 4:14 warning: unused variable: `C`, #[warn(unused_variables)] on by default
<anon>:4         C @ 2 => { println!("{}", C); }
                 ^~~~~
Switch constants must all be same type as switch value!
  switch i32 %3, label %match_else [
    i8 3, label %match_case
  ]
LLVM ERROR: Broken function found, compilation aborted!
playpen: application terminated with error code 1

Not sure how this is happening and the code should be rejected as in #27033, but it does indicate that something in the compiler is probably broken.

cc @rust-lang/compiler

[arielb1]

This is a wrong-codegen bug:

fn f(x: Option<u32>) {
    const C: Option<u32> = None;
    match x {
        C @ Some(x) => { println!("{}", x); }
        _ => {}
    }
}
fn main() { f(None) }