In #41365 we saw a travis failure because a URL was not a valid gz - https://travis-ci.org/rust-lang/rust/jobs/223417092#L991.

https://fuchsia.googlesource.com/third_party/llvm/+archive/5463083.tar.gz seems dead.

While the docker image is reused from the cache we can get by, but this is probably going to start blocking the queue shortly (I'm not currently clear what caused the linked PR to do the rebuild).

ping @tedsta @raphlinus