Always include <sys/cdefs.h> first.

Otherwise you can't be sure that things like __BIONIC__ work.

Change-Id: Ic5e59988b69419828c3b1a97332c7e2ab58e09a1
diff --git a/libc/include/sys/wait.h b/libc/include/sys/wait.h
index 5208366..632aa43 100644
--- a/libc/include/sys/wait.h
+++ b/libc/include/sys/wait.h
@@ -28,8 +28,9 @@
 
 #pragma once
 
-#include <bits/wait.h>
 #include <sys/cdefs.h>
+
+#include <bits/wait.h>
 #include <sys/types.h>
 #include <sys/resource.h>
 #include <linux/wait.h>