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/uchar.h b/libc/include/uchar.h
index 55a36e7..94efb2d 100644
--- a/libc/include/uchar.h
+++ b/libc/include/uchar.h
@@ -33,9 +33,10 @@
  * @brief Unicode functions.
  */
 
-#include <stddef.h>
 #include <sys/cdefs.h>
 
+#include <stddef.h>
+
 #include <bits/bionic_multibyte_result.h>
 #include <bits/mbstate_t.h>