Unideal log for PR 49913

[varkor]

rust-lang/rust#49913 (comment)

https://travis-ci.org/rust-lang/rust/jobs/365860984

Ideally, the error message would have included:

Testing rustc_driver stage1 (x86_64-unknown-linux-gnu -> x86_64-unknown-linux-gnu)
[01:18:27]    Compiling rustc_driver v0.0.0 (file:///checkout/src/librustc_driver)
[01:18:29] error[E0308]: mismatched types
[01:18:29]    --> librustc_driver/test.rs:314:13
[01:18:29]     |

which is necessary to debug the issue.