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/dlfcn.h b/libc/include/dlfcn.h
index 071d50a..1b0d11b 100644
--- a/libc/include/dlfcn.h
+++ b/libc/include/dlfcn.h
@@ -28,9 +28,10 @@
 
 #pragma once
 
-#include <stdint.h>
 #include <sys/cdefs.h>
 
+#include <stdint.h>
+
 __BEGIN_DECLS
 
 /**