internal compiler error: unrecognized builtin nonterminal elem

[Kroisse]

Example:

macro_rules! weird {
    ($a:elem, $b:expr) => {}
}

fn main() {
    weird!(a, b);
}

Compiler message:

error: internal compiler error: unrecognized builtin nonterminal elem
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /build/rust-git/src/rust/src/libsyntax/diagnostic.rs:185

[jdm]

Dup of #21356.