Clean the docs before building. Log rustc failures
Clean the docs before building. Log rustc failures

aidanhs/rust-buildbot,rust-lang/rust-buildbot,rust-lang/rust-buildbot,aidanhs/rust-buildbot,aidanhs/rust-buildbot,rust-lang-deprecated/rust-buildbot,edunham/rust-buildbot,edunham/rust-buildbot,rust-lang/rust-buildbot,rust-lang-deprecated/rust-buildbot,edunham/rust-buildbot,rust-lang-deprecated/rust-buildbot