[Cherry Pick] lock: Avoid use of undefined DISPATCH_INTERNAL_CRASH#241

MadCoder merged 1 commit intoswiftlang:swift-3.1-branchswiftlang/swift-corelibs-libdispatch:swift-3.1-branchfrom

ffried:swift-3.1-branchffried/swift-corelibs-libdispatch:swift-3.1-branchCopy head branch name to clipboard