Re-merge darwin/libdispatch-890 to master#256

das merged 2 commits intomasterswiftlang/swift-corelibs-libdispatch:masterfrom

revert-255-revert-254-das-darwin-libdispatch-890-merge-masterswiftlang/swift-corelibs-libdispatch:revert-255-revert-254-das-darwin-libdispatch-890-merge-masterCopy head branch name to clipboard