Missing #include <sys/cdefs.h>.

Needed for __BEGIN_DECLS/__END_DECLS. Currently fine because it's being
included after other files that do this.

Change-Id: I1f12368fc461f6ef5ca90992cf19f317f0b5d7af
diff --git a/libc/include/android/set_abort_message.h b/libc/include/android/set_abort_message.h
index 3e6da1f..4b3d82b 100644
--- a/libc/include/android/set_abort_message.h
+++ b/libc/include/android/set_abort_message.h
@@ -29,6 +29,8 @@
 #ifndef _SET_ABORT_MESSAGE_H
 #define _SET_ABORT_MESSAGE_H
 
+#include <sys/cdefs.h>
+
 __BEGIN_DECLS
 
 void android_set_abort_message(const char* msg);