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/libc/aos_strsignal.cc b/aos/libc/aos_strsignal.cc
index 91c2211..0f9b065 100644
--- a/aos/libc/aos_strsignal.cc
+++ b/aos/libc/aos_strsignal.cc
@@ -1,10 +1,9 @@
 #include "aos/libc/aos_strsignal.h"
 
-#include <signal.h>
-
-#include "glog/logging.h"
+#include <csignal>
 
 #include "aos/thread_local.h"
+#include "glog/logging.h"
 
 const char *aos_strsignal(int signal) {
   AOS_THREAD_LOCAL char buffer[512];