Nonexisting macro is silently accepted in trait definition block

[bluss]

This compiles successfully on beta and nightly, but it should be an error.

trait Trait {
    wut!{ }
}

fn main() {
}

(playground link)

Actual Result:

The program compiles successfully.

Expected Result:

Compilation error (Rust 1.16 does this correctly)

rustc 1.16.0 (30cf806ef 2017-03-10)
error: macro undefined: 'wut!'

[jseyfried]

Fixed in #40849.