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/bits/swab.h b/libc/include/bits/swab.h
index 9591c2e..da2865a 100644
--- a/libc/include/bits/swab.h
+++ b/libc/include/bits/swab.h
@@ -28,8 +28,9 @@
 
 #pragma once
 
-#include <stdint.h>
 #include <sys/cdefs.h>
+
+#include <stdint.h>
 #include <sys/types.h>
 
 #if !defined(__BIONIC_SWAB_INLINE)