io-util: introduce ppoll_usec() helper function

src/basic/io-util.h

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 #pragma once
 
+#include <poll.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -18,6 +19,7 @@ int loop_write(int fd, const void *buf, size_t nbytes, bool do_poll);
 
 int pipe_eof(int fd);
 
+int ppoll_usec(struct pollfd *fds, size_t nfds, usec_t timeout);
 int fd_wait_for_event(int fd, int event, usec_t timeout);
 
 ssize_t sparse_write(int fd, const void *p, size_t sz, size_t run_length);