add build of lib/dns/dnsrps.c to CI
A recent freebsd build failed in lib/dns/dnsrps.c because a recent change left a variable unused and this was only detected on Jenkins after the merge, not in the CI.
A recent freebsd build failed in lib/dns/dnsrps.c because a recent change left a variable unused and this was only detected on Jenkins after the merge, not in the CI.