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.

third_party/nsync/mu_semaphore_gcd.c

@@ -20,6 +20,7 @@
 #include "libc/errno.h"
 #include "libc/intrin/strace.internal.h"
 #include "libc/intrin/weaken.h"
+#include "libc/runtime/clktck.h"
 #include "libc/runtime/syslib.internal.h"
 #include "libc/str/str.h"
 #include "libc/thread/posixthread.internal.h"
@@ -116,8 +117,7 @@ errno_t nsync_mu_semaphore_p_with_deadline_gcd (nsync_semaphore *s,
 	    (pt->pt_flags & PT_NOCANCEL)) {
 		result = nsync_dispatch_semaphore_wait (s, abs_deadline);
 	} else {
-		struct timespec now, until, slice;
-		slice = timespec_frommillis (__SIG_LOCK_INTERVAL_MS);
+		struct timespec now, until, slice = {0, 1000000000 / CLK_TCK};
 		for (;;) {
 			if (_weaken (pthread_testcancel_np) () == ECANCELED) {
 				result = ECANCELED;