% grep -r __attribute__ lib/isc/include/
lib/isc/include/isc/formatcheck.h:#define ISC_FORMAT_PRINTF(fmt, args) __attribute__((__format__(__printf__, fmt, args)))
lib/isc/include/isc/platform.h:#define ISC_PLATFORM_NORETURN_POST __attribute__((noreturn))
lib/isc/include/isc/util.h:#define ISC_DEPRECATED			__attribute__((deprecated))
% 

<isc/deprecated.h> would be much more appropriate.  <isc/util.h> pulls in too
much baggage for users of libisc, libdns etc.