Dead code check false positive for static used in match

[jfager]

With #10477 landed, the following snippet complains that FOO is unused:

static FOO: u16 = 1;

fn main() {
    let i = 1;
    match i {
        FOO => println!("matched"),
        _ => println!("unmatched")
    }
}

[huonw]

cc @ktt3ja

[ktt3ja]

Thanks.