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/calls/readwrite-nt.c

@@ -33,6 +33,7 @@
 #include "libc/nt/synchronization.h"
 #include "libc/nt/thread.h"
 #include "libc/stdio/sysparam.h"
+#include "libc/str/str.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/errfuns.h"
 #include "libc/thread/posixthread.internal.h"
@@ -67,10 +68,10 @@ sys_readwrite_nt(int fd, void *data, size_t size, ssize_t offset,
   bool32 ok;
   uint64_t m;
   uint32_t exchanged;
+  int olderror = errno;
   bool eagained = false;
   bool eintered = false;
   bool canceled = false;
-  bool olderror = errno;
   struct PosixThread *pt;
   struct Fd *f = g_fds.p + fd;
 
@@ -124,7 +125,7 @@ sys_readwrite_nt(int fd, void *data, size_t size, ssize_t offset,
   // can only be returned by a single system call in a thread's life
   // another thing we do is check if any pending signals exist, then
   // running as many of them as possible before entering a wait call
-  struct NtOverlapped overlap = {.hEvent = CreateEvent(0, 0, 0, 0),
+  struct NtOverlapped overlap = {.hEvent = CreateEvent(0, 1, 0, 0),
                                  .Pointer = offset};
   struct ReadwriteResources rwc = {handle, &overlap};
   pthread_cleanup_push(UnwindReadwrite, &rwc);