CORK_ATTR_SENTINEL attribute macro
CORK_ATTR_SENTINEL attribute macro

This patch adds a CORK_ATTR_SENTINEL macro that can be used to define a
function whose parameter list must be terminated with an explicit NULL
sentinel value.

dcreager/libcork,tempbottle/libcork,redjack/libcork,rogers0/libcork,tempbottle/libcork,dcreager/libcork,rogers0/libcork,ifduyue/libcork,rogers0/libcork,rogers0/libcork,dcreager/libcork,dcreager/libcork,redjack/libcork,tempbottle/libcork,tempbottle/libcork,dcreager/libcork,tempbottle/libcork,ifduyue/libcork,ifduyue/libcork,redjack/libcork,redjack/libcork,ifduyue/libcork,redjack/libcork,ifduyue/libcork,ifduyue/libcork,redjack/libcork,rogers0/libcork,tempbottle/libcork,rogers0/libcork