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/stdlib.h b/libc/include/stdlib.h
index 076a978..2c918d4 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -29,11 +29,12 @@
 #ifndef _STDLIB_H
 #define _STDLIB_H
 
+#include <sys/cdefs.h>
+
 #include <alloca.h>
 #include <bits/wait.h>
 #include <malloc.h>
 #include <stddef.h>
-#include <sys/cdefs.h>
 #include <xlocale.h>
 
 __BEGIN_DECLS