sys/capability.h will be removed before FreeBSD 13. The (now) correct header to use on all supported (and most unsupported) versions of FreeBSD is sys/capsicum.h. There's no need for autoconf checks etc. to check for both (in the ports tree) but upstream may want to if there's a desire to build on older releases. work/dnscrypt-proxy-2.0.17/vendor/golang.org/x/sys/unix/types_freebsd.go 25:#include <sys/capability.h>
Maintainer informed via mail
It appears this is simply a side-effect of go's use of capability.h - see PR 233092.
grep of the source-code for "capsicum.h" shows usr/ports/dns/dnscrypt-proxy2/work/dnscrypt-proxy-2.0.19/vendor/golang.org/x/sys/unix/mkerrors.sh:#include <sys/capsicum.h> /usr/ports/dns/dnscrypt-proxy2/work/dnscrypt-proxy-2.0.19/vendor/golang.org/x/sys/unix/types_freebsd.go:#include <sys/capsicum.h> And no output for "capability.h". So I close here, with overcome by events.