Add support for clock syscalls

buildtest.c

@@ -50,6 +50,14 @@ int main() {
   } else {
     write(STDOUT, "Could not open /proc/version\n", 29);
   }
+
+  // Test sleep
+  write(STDOUT, "Sleeping for 5 secs\n", 20);
+  struct timespec sleeptime;
+  sleeptime.tv_sec = 5;
+  while (nanosleep(&sleeptime, &sleeptime) != 0) {}
+  write(STDOUT, "DONE\n", 5);
+
   return 69;
 }