Fix some small divergences from Darwin overlay

A collection of small fixes to eliminate needless
differences (as reported by diff -r -b) between
swift/stdlib/public/SDK/Dispatch and
swift-corelibs-libdispatch/src/swift.

Signed-off-by: Daniel A. Steffen <dsteffen@apple.com>

Author: dgrove-oss

src/swift/Block.swift

@@ -37,14 +37,13 @@ public struct DispatchWorkItemFlags : OptionSet, RawRepresentable {
 @available(OSX 10.10, iOS 8.0, *)
 public class DispatchWorkItem {
 	internal var _block: _DispatchBlock
-	internal var _group: DispatchGroup?
 
 	public init(qos: DispatchQoS = .unspecified, flags: DispatchWorkItemFlags = [], block: @escaping @convention(block) () -> ()) {
 		_block =  dispatch_block_create_with_qos_class(dispatch_block_flags_t(flags.rawValue),
 			qos.qosClass.rawValue.rawValue, Int32(qos.relativePriority), block)
 	}
 
-	// Used by DispatchQueue.synchronously<T> to provide a @noescape path through
+	// Used by DispatchQueue.synchronously<T> to provide a path through
 	// dispatch_block_t, as we know the lifetime of the block in question.
 	internal init(flags: DispatchWorkItemFlags = [], noescapeBlock: () -> ()) {
 		_block = _swift_dispatch_block_create_noescape(dispatch_block_flags_t(flags.rawValue), noescapeBlock)

src/swift/Data.swift

@@ -49,7 +49,6 @@ public struct DispatchData : RandomAccessCollection {
 	/// Initialize a `Data` with copied memory content.
 	///
 	/// - parameter bytes: A pointer to the memory. It will be copied.
-	/// - parameter count: The number of bytes to copy.
 	public init(bytes buffer: UnsafeBufferPointer<UInt8>) {
 		let d = dispatch_data_create(buffer.baseAddress!, buffer.count, nil, _dispatch_data_destructor_default())
 		self.init(data: d)
@@ -88,7 +87,7 @@ public struct DispatchData : RandomAccessCollection {
 	public func enumerateBytes(
 		block: @noescape (_ buffer: UnsafeBufferPointer<UInt8>, _ byteIndex: Int, _ stop: inout Bool) -> Void)
 	{
-		_swift_dispatch_data_apply(__wrapped.__wrapped) { (data: dispatch_data_t, offset: Int, ptr: UnsafeRawPointer, size: Int) in
+		_swift_dispatch_data_apply(__wrapped.__wrapped) { (_, offset: Int, ptr: UnsafeRawPointer, size: Int) in
 			let bytePtr = ptr.bindMemory(to: UInt8.self, capacity: size)
 			let bp = UnsafeBufferPointer(start: bytePtr, count: size)
 			var stop = false
@@ -124,7 +123,7 @@ public struct DispatchData : RandomAccessCollection {
 		}
 	}
 
-	private func _copyBytesHelper(to pointer: UnsafeMutablePointer<UInt8>, from range: CountableRange<Index>) {
+	private func _copyBytesHelper(to pointer: UnsafeMutableRawPointer, from range: CountableRange<Index>) {
 		var copiedCount = 0
 		_ = CDispatch.dispatch_data_apply(__wrapped.__wrapped) { (data: dispatch_data_t, offset: Int, ptr: UnsafeRawPointer, size: Int) in
 			let limit = Swift.min((range.endIndex - range.startIndex) - copiedCount, size)
@@ -244,7 +243,7 @@ public struct DispatchData : RandomAccessCollection {
 
 public struct DispatchDataIterator : IteratorProtocol, Sequence {
 
-	/// Create an iterator over the given DisaptchData
+	/// Create an iterator over the given DispatchData
 	public init(_data: DispatchData) {
 		var ptr: UnsafeRawPointer?
 		self._count = 0

src/swift/Wrapper.swift

@@ -153,7 +153,7 @@ public class DispatchQueue : DispatchObject {
 		_swift_dispatch_release(wrapped())
 	}
 
-	public func sync(execute workItem: @noescape ()->()) {
+	public func sync(execute workItem: ()->()) {
 		dispatch_sync(self.__wrapped, workItem)
 	}
 }