Add epoll and do more release readiness changes

This change also pays off some of the remaining technical debt with
stdio, file descriptors, and memory managemnt polyfills.

libc/stdio/scanf.c

@@ -28,7 +28,7 @@ int(scanf)(const char *fmt, ...) {
   int rc;
   va_list va;
   va_start(va, fmt);
-  rc = (vcscanf)((int (*)(void *))fgetc, stdin, fmt, va);
+  rc = (vcscanf)((int (*)(void *))fgetc, NULL, stdin, fmt, va);
   va_end(va);
   return rc;
 }