Rollup of 6 pull requests#42012

Closed

frewsxcv wants to merge 16 commits intorust-lang:masterfrom

frewsxcv:rollup

Commits on May 14, 2017

Explain why `thread::yield_now` could be used.
Felix Raimundo
committed
Improve `thread::Builder` documentation.
Felix Raimundo
committed
Remove rustc_llvm dependency from rustc_metadata
Robin Kruppe
committed
appveyor: Wrap handle.exe download in a retry
alexcrichton
committed

Commits on May 15, 2017