ensure root_queues are initialized before main thread exits
ensure root_queues are initialized before main thread exits

apple/swift-corelibs-libdispatch,frankeh/swift-corelibs-libdispatch,frankeh/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,frankeh/swift-corelibs-libdispatch,frankeh/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch