ICE when using 'match' on enum parameter inside const function

[frewsxcv]

#![feature(const_fn)]

pub enum A {
    B,
    C,
}

const fn foo(a: A) {
    match a {
        A::B => (),
        A::C => (),
    }
}

fn main() {}

playpen: https://is.gd/n7pDFb

rustc 1.17.0-nightly (e703b33e3 2017-03-23)
error: internal compiler error: /checkout/src/librustc_mir/transform/qualify_consts.rs:733: implement discriminant const qualify

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

thread 'rustc' panicked at 'Box<Any>', /checkout/src/librustc_errors/lib.rs:418
note: Run with `RUST_BACKTRACE=1` for a backtrace.

[frewsxcv]

Duplicate of #40012