[swift] Stop using _SwiftDispatchOverlayShims#592

lorentey merged 1 commit intomainswiftlang/swift-corelibs-libdispatch:mainfrom

lorentey/stop-using-toolchain-shimsswiftlang/swift-corelibs-libdispatch:lorentey/stop-using-toolchain-shimsCopy head branch name to clipboard