Replace use of deprecated C Standard library headers in C++ code.

Change-Id: I9fa6630c7e4bdb2897df34d417635d8c7d8253bc
Signed-off-by: Tyler Chatow <tchatow@gmail.com>
diff --git a/aos/ipc_lib/signal_stress.cc b/aos/ipc_lib/signal_stress.cc
index 2f2ca41..57a4158 100644
--- a/aos/ipc_lib/signal_stress.cc
+++ b/aos/ipc_lib/signal_stress.cc
@@ -1,8 +1,7 @@
-#include "gflags/gflags.h"
-
-#include <signal.h>
 #include <sys/signalfd.h>
+
 #include <chrono>
+#include <csignal>
 #include <random>
 #include <thread>
 
@@ -13,6 +12,7 @@
 #include "aos/logging/logging.h"
 #include "aos/realtime.h"
 #include "aos/time/time.h"
+#include "gflags/gflags.h"
 
 // This is a demo program which uses Real-Time posix signals to communicate.
 // It measures both latency of a random timer thread, and latency of the