Reintroduce crossbeam threads
Reintroduce crossbeam threads

Turns out, these are actually necessary -- we will deadlock otherwise, though
it's not entirely obvious why.

tshepang/cargo,tshepang/cargo,tsurai/cargo,rust-lang/cargo,tshepang/cargo,nipunn1313/cargo,eminence/cargo,eminence/cargo,vojtechkral/cargo,rustyhorde/cargo,tsurai/cargo,nipunn1313/cargo,tshepang/cargo,vojtechkral/cargo,tsurai/cargo,eminence/cargo,tsurai/cargo,rustyhorde/cargo,vojtechkral/cargo,nipunn1313/cargo,tsurai/cargo,eminence/cargo,rust-lang/cargo,rust-lang/cargo,rustyhorde/cargo,rustyhorde/cargo,rust-lang/cargo,nipunn1313/cargo,vojtechkral/cargo