Fix bugs in poll(), select(), ppoll(), and pselect()

poll() and select() now delegate to ppoll() and pselect() for assurances
that both polyfill implementations are correct and well-tested. Poll now
polyfills XNU and BSD quirks re: the hanndling of POLLNVAL and the other
similar status flags. This change resolves a misunderstanding concerning
how select(exceptfds) is intended to map to POLPRI. We now use E2BIG for
bouncing requests that exceed the 64 handle limit on Windows. With pipes
and consoles on Windows our poll impl will now report POLLHUP correctly.

Issues with Windows path generation have been fixed. For example, it was
problematic on Windows to say: posix_spawn_file_actions_addchdir_np("/")
due to the need to un-UNC paths in some additional places. Calling fstat
on UNC style volume path handles will now work. posix_spawn now supports
simulating the opening of /dev/null and other special paths on Windows.

Cosmopolitan no longer defines epoll(). I think wepoll is a nice project
for using epoll() on Windows socket handles. However we need generalized
file descriptor support to make epoll() for Windows work well enough for
inclusion in a C library. It's also not worth having epoll() if we can't
get it to work on XNU and BSD OSes which provide different abstractions.
Even epoll() on Linux isn't that great of an abstraction since it's full
of footguns. Last time I tried to get it to be useful I had little luck.
Considering how long it took to get poll() and select() to be consistent
across platforms, we really have no business claiming to have epoll too.
While it'd be nice to have fully implemented, the only software that use
epoll() are event i/o libraries used by things like nodejs. Event i/o is
not the best paradigm for handling i/o; threads make so much more sense.

libc/calls/select.c

@@ -17,26 +17,25 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/sock/select.h"
-#include "libc/calls/cp.internal.h"
-#include "libc/calls/struct/itimerval.internal.h"
-#include "libc/calls/struct/timespec.h"
 #include "libc/calls/struct/timeval.h"
-#include "libc/calls/struct/timeval.internal.h"
-#include "libc/dce.h"
-#include "libc/intrin/describeflags.h"
-#include "libc/intrin/strace.h"
-#include "libc/sock/internal.h"
-#include "libc/sock/select.h"
-#include "libc/sock/select.internal.h"
-#include "libc/sysv/errfuns.h"
 
 /**
- * Does what poll() does except with bitset API.
- *
- * This system call is supported on all platforms. However, on Windows,
- * this is polyfilled to translate into poll(). So it's recommended that
- * poll() be used instead.
+ * Checks status on multiple file descriptors at once.
  *
+ * @param readfds may be used to be notified when you can call read() on
+ *     a file descriptor without it blocking; this includes when data is
+ *     is available to be read as well as eof and error conditions
+ * @param writefds may be used to be notified when write() may be called
+ *     on a file descriptor without it blocking
+ * @param exceptfds may be used to be notified of exceptional conditions
+ *     such as out-of-band data on a socket; it is equivalent to POLLPRI
+ *     in the revents of poll()
+ * @param timeout may be null which means to block indefinitely; cosmo's
+ *     implementation of select() never modifies this parameter which is
+ *     how most platforms except Linux work which modifies it to reflect
+ *     elapsed time, noting that POSIX permits either behavior therefore
+ *     portable code should assume that timeout memory becomes undefined
+ * @raise E2BIG if we exceeded the 64 socket limit on Windows
  * @raise ECANCELED if thread was cancelled in masked mode
  * @raise EINTR if signal was delivered
  * @cancelationpoint
@@ -45,70 +44,13 @@
  */
 int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
            struct timeval *timeout) {
-
-  int rc;
-  fd_set old_readfds;
-  fd_set *old_readfds_ptr = 0;
-  fd_set old_writefds;
-  fd_set *old_writefds_ptr = 0;
-  fd_set old_exceptfds;
-  fd_set *old_exceptfds_ptr = 0;
-  struct timeval old_timeout;
-  struct timeval *old_timeout_ptr = 0;
-
-  POLLTRACE("select(%d, %p, %p, %p, %s) → ...", nfds, readfds, writefds,
-            exceptfds, DescribeTimeval(0, timeout));
-
-  BEGIN_CANCELATION_POINT;
-  if (nfds < 0) {
-    rc = einval();
+  struct timespec ts;
+  struct timespec *tsp;
+  if (timeout) {
+    ts = timeval_totimespec(*timeout);
+    tsp = &ts;
   } else {
-    if (readfds) {
-      old_readfds = *readfds;
-      old_readfds_ptr = &old_readfds;
-    }
-    if (writefds) {
-      old_writefds = *writefds;
-      old_writefds_ptr = &old_writefds;
-    }
-    if (exceptfds) {
-      old_exceptfds = *exceptfds;
-      old_exceptfds_ptr = &old_exceptfds;
-    }
-    if (timeout) {
-      old_timeout = *timeout;
-      old_timeout_ptr = &old_timeout;
-    }
-    if (!IsWindows()) {
-#ifdef __aarch64__
-      struct timespec ts, *tsp;
-      if (timeout) {
-        ts = timeval_totimespec(*timeout);
-        tsp = &ts;
-      } else {
-        tsp = 0;
-      }
-      rc = sys_pselect(nfds, readfds, writefds, exceptfds, tsp, 0);
-      if (timeout) {
-        *timeout = timespec_totimeval(ts);
-      }
-#else
-      rc = sys_select(nfds, readfds, writefds, exceptfds, timeout);
-#endif
-    } else {
-      rc = sys_select_nt(nfds, readfds, writefds, exceptfds, timeout, 0);
-    }
+    tsp = 0;
   }
-  END_CANCELATION_POINT;
-
-  STRACE("select(%d, %s → [%s], %s → [%s], %s → [%s], %s → [%s]) → %d% m", nfds,
-         DescribeFdSet(rc, nfds, old_readfds_ptr),
-         DescribeFdSet(rc, nfds, readfds),
-         DescribeFdSet(rc, nfds, old_writefds_ptr),
-         DescribeFdSet(rc, nfds, writefds),
-         DescribeFdSet(rc, nfds, old_exceptfds_ptr),
-         DescribeFdSet(rc, nfds, exceptfds),    //
-         DescribeTimeval(rc, old_timeout_ptr),  //
-         DescribeTimeval(rc, timeout), rc);
-  return rc;
+  return pselect(nfds, readfds, writefds, exceptfds, tsp, 0);
 }