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/panic.c

@@ -17,12 +17,17 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
-#include "libc/str/str.h"
+#include "libc/errno.h"
+#include "libc/intrin/describebacktrace.internal.h"
+#include "libc/runtime/runtime.h"
 #include "third_party/nsync/common.internal.h"
 // clang-format off
 
 /* Aborts after printing the nul-terminated string s[]. */
 void nsync_panic_ (const char *s) {
-	tinyprint (2, "nsync panic: ", s, NULL);
-	notpossible;
+	tinyprint(2, "error: nsync panic: ", s, "\n",
+		"cosmoaddr2line ", program_invocation_name, " ",
+		DescribeBacktrace (__builtin_frame_address (0)), "\n",
+		NULL);
+	_Exit (44);
 }