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.

test/libc/thread/pthread_kill_test.c

@@ -21,6 +21,7 @@
 #include "libc/calls/struct/sigaction.h"
 #include "libc/dce.h"
 #include "libc/errno.h"
+#include "libc/intrin/kprintf.h"
 #include "libc/runtime/runtime.h"
 #include "libc/sock/sock.h"
 #include "libc/sock/struct/sockaddr.h"
@@ -61,7 +62,7 @@ void OnSig(int sig) {
 void WaitUntilReady(void) {
   while (!ready) pthread_yield();
   ASSERT_EQ(0, errno);
-  ASSERT_SYS(0, 0, usleep(1000));
+  ASSERT_SYS(0, 0, usleep(100000));
 }
 
 void *SleepWorker(void *arg) {