Test in libsyntax doesn't call abort_if_errors

[pcwalton]

As per https://github.com/pcwalton/rust/blob/6f98fa372d898932c3420a92da581c8fa6342ab0/src/libsyntax/parse/mod.rs#L479

The test causes a parse error, but this isn't turned into a failure-failure properly (requires calling abort_if_errors) so the #[should_fail] annotation doesn't work right. The parse "succeeds".

[graydon]

Visiting for triage. Reproduced, rewrite bug to reflect proper state of affairs. Made fix. Testing now, PR in the queue.