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/bionic_multibyte_result.h b/libc/include/bits/bionic_multibyte_result.h
index 0d5cf21..930e67c 100644
--- a/libc/include/bits/bionic_multibyte_result.h
+++ b/libc/include/bits/bionic_multibyte_result.h
@@ -34,9 +34,10 @@
  * conversion APIs defined by C.
  */
 
-#include <stddef.h>
 #include <sys/cdefs.h>
 
+#include <stddef.h>
+
 __BEGIN_DECLS
 
 /**