tools/nolibc/unistd: add usleep()

This call is trivial to implement based on select() to complete sleep()
and msleep(), let's add it.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/include/nolibc/unistd.h

@@ -37,6 +37,14 @@ unsigned int sleep(unsigned int seconds)
 		return 0;
 }
 
+static __attribute__((unused))
+int usleep(unsigned int usecs)
+{
+	struct timeval my_timeval = { usecs / 1000000, usecs % 1000000 };
+
+	return sys_select(0, 0, 0, 0, &my_timeval);
+}
+
 static __attribute__((unused))
 int tcsetpgrp(int fd, pid_t pid)
 {