Rewrite Windows poll()

We can now await signals, files, pipes, and console simultaneously. This
change also gives a deeper review and testing to changes made yesterday.

libc/thread/pthread_cond_init.c

@@ -30,11 +30,8 @@ errno_t pthread_cond_init(pthread_cond_t *cond,
                           const pthread_condattr_t *attr) {
   *cond = (pthread_cond_t){0};
   if (attr) {
-    cond->_footek = IsXnuSilicon() || attr->_pshared;
     cond->_pshared = attr->_pshared;
     cond->_clock = attr->_clock;
-  } else {
-    cond->_footek = IsXnuSilicon();
   }
   return 0;
 }