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/sock/bind-nt.c

@@ -16,20 +16,16 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/assert.h"
-#include "libc/calls/struct/fd.internal.h"
 #include "libc/nt/thunk/msabi.h"
-#include "libc/nt/winsock.h"
 #include "libc/sock/internal.h"
 #include "libc/sock/syscall_fd.internal.h"
 #ifdef __x86_64__
 
 __msabi extern typeof(__sys_bind_nt) *const __imp_bind;
 
-textwindows int sys_bind_nt(struct Fd *fd, const void *addr,
-                            uint32_t addrsize) {
-  unassert(fd->kind == kFdSocket);
-  if (__imp_bind(fd->handle, addr, addrsize) != -1) {
+textwindows int sys_bind_nt(struct Fd *f, const void *addr, uint32_t addrsize) {
+  if (__imp_bind(f->handle, addr, addrsize) != -1) {
+    f->isbound = true;
     return 0;
   } else {
     return __winsockerr();