Improve threading and i/o routines

- On Windows connect() can now be interrupted by a signal; connect() w/
  O_NONBLOCK will now raise EINPROGRESS; and connect() with SO_SNDTIMEO
  will raise ETIMEDOUT after the interval has elapsed.

- We now get the AcceptEx(), ConnectEx(), and TransmitFile() functions
  from the WIN32 API the officially blessed way, using WSAIoctl().

- Do nothing on Windows when fsync() is called on a directory handle.
  This was raising EACCES earlier becaues GENERIC_WRITE is required on
  the handle. It's possible to FlushFileBuffers() a directory handle if
  it's opened with write access but MSDN doesn't document what it does.
  If you have any idea, please let us know!

- Prefer manual reset event objects for read() and write() on Windows.

- Do some code cleanup on our dlmalloc customizations.

- Fix errno type error in Windows blocking routines.

- Make the futex polyfill simpler and faster.

libc/nt/iocp.h

@@ -39,13 +39,13 @@ typedef void (*NtOverlappedCompletionRoutine)(
 
 int64_t CreateIoCompletionPort(int64_t FileHandleOrNeg1,
                                int64_t opt_ExistingCompletionPortOrZero,
-                               void *StatePointer,
+                               uint64_t CompletionKey,
                                uint32_t NumberOfConcurrentThreads);
 
 bool32 GetQueuedCompletionStatus(int64_t CompletionPort,
                                  uint32_t *lpNumberOfBytesTransferred,
-                                 void *StatePointerPointer,
-                                 struct NtOverlapped **lpOverlapped,
+                                 uint64_t *out_lpCompletionKey,
+                                 struct NtOverlapped **out_lpOverlapped,
                                  uint32_t dwMilliseconds);
 
 bool32 GetQueuedCompletionStatusEx(
@@ -56,7 +56,7 @@ bool32 GetQueuedCompletionStatusEx(
 
 bool32 PostQueuedCompletionStatus(int64_t CompletionPort,
                                   uint32_t dwNumberOfBytesTransferred,
-                                  uint32_t *dwCompletionKey,
+                                  uint64_t dwCompletionKey,
                                   struct NtOverlapped *opt_lpOverlapped);
 
 bool32 SetFileCompletionNotificationModes(int64_t FileHandle,