Ensure header files using __BEGIN_DECLS include sys/cdefs.h.

We keep fixing these one-by-one; let's fix them all at once.

Found thus:

  find . -name *.h | xargs grep -L sys/cdefs.h | xargs grep -l BEGIN_DECL | xargs grep -L sys/types

Change-Id: I188842aa2484dc6176e96556d57c38a0f785b59b
diff --git a/libc/private/resolv_private.h b/libc/private/resolv_private.h
index 0f3c6c0..c43c84c 100644
--- a/libc/private/resolv_private.h
+++ b/libc/private/resolv_private.h
@@ -54,6 +54,8 @@
 #ifndef _RESOLV_PRIVATE_H_
 #define	_RESOLV_PRIVATE_H_
 
+#include <sys/cdefs.h>
+
 #include <resolv.h>
 #include "resolv_static.h"