It only affects gcc-2 and non-gcc (which is untested anyway).
# define __noreturn /* no noreturn */
# define __malloc /* no malloc */
# define __used /* no used */
# define __noreturn /* no noreturn */
# define __malloc /* no malloc */
# define __used /* no used */
-# define __a__unused /* no unused */
+# define __a_unused /* no unused */
# define __packed /* no packed */
# define likely(x) (x)
# define unlikely(x) (x)
# define __packed /* no packed */
# define likely(x) (x)
# define unlikely(x) (x)