www/mohawk: unbreak on 12.0 after r312758

In file included from parse.c:17:
In file included from parse.y:34:
/usr/include/sys/capability.h:41:2: error: this file includes <sys/capability.h> which is deprecated [-Werror,-W#warnings]
#warning this file includes <sys/capability.h> which is deprecated

^

Reported by: pkg-fallout