Rollup merge of #41741 - rap2hpoutre:patch-3, r=steveklabnik

join method returns a thread::Result

Join method returns a std::thread::Result, not a std::result::Result: https://doc.rust-lang.org/std/thread/struct.JoinHandle.html#method.join Maybe I misunderstood something.

I have seen this mistake(?) because I wanted to tackle this issue https://github.com/rust-lang/rust/issues/29378 (about Result). It's still one of my first PR. Sorry if I missed something.