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/dlmalloc/dlmalloc_abort.c

@@ -0,0 +1,32 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/errno.h"
+#include "libc/intrin/describebacktrace.internal.h"
+#include "libc/runtime/runtime.h"
+#include "third_party/dlmalloc/dlmalloc.h"
+
+void dlmalloc_abort(void) {
+  tinyprint(2,
+            "error: dlmalloc aborted\n"
+            "cosmoaddr2line ",
+            program_invocation_name, " ",
+            DescribeBacktrace(__builtin_frame_address(0)), "\n", NULL);
+  _Exit(44);
+}