New relay unit test code fails to link using libtool under Fedora 30/Centos 8

Build farm failed to build on Fedora30 (and Centos 8) when trying to link the new unit test binary, relay/tests/relay_unitttest:

libtool: link: gcc -g -O2 -I../../../../includes -I/home/jenkins/workspace/isc-dhcp-master-distcheck/LIBTOOL/True/label/fedora-64-latest/dhcp-4.4.2b1/bind/include -o .libs/relay_unittests dhcrelay.o relay_unittests.o  -L/opt/atf/lib /opt/atf/lib/libatf-c.a ../../common/.libs/libdhcp.so ../../omapip/.libs/libomapi.so /home/jenkins/workspace/isc-dhcp-master-distcheck/LIBTOOL/True/label/fedora-64-latest/dhcp-4.4.2b1/bind/bind-9.11.14/lib/irs/.libs/libirs.so /home/jenkins/workspace/isc-dhcp-master-distcheck/LIBTOOL/True/label/fedora-64-latest/dhcp-4.4.2b1/bind/bind-9.11.14/lib/isccfg/.libs/libisccfg.so /home/jenkins/workspace/isc-dhcp-master-distcheck/LIBTOOL/True/label/fedora-64-latest/dhcp-4.4.2b1/bind/bind-9.11.14/lib/dns/.libs/libdns.so /home/jenkins/workspace/isc-dhcp-master-distcheck/LIBTOOL/True/label/fedora-64-latest/dhcp-4.4.2b1/bind/bind-9.11.14/lib/isc/.libs/libisc.so -ldl -lcap -lz -Wl,-rpath -Wl,/home/jenkins/workspace/isc-dhcp-master-distcheck/LIBTOOL/True/label/fedora-64-latest/dhcp-4.4.2b1/_inst/lib
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `find_class'
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `classify'
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `dhcpv6'
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `check_collection'
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `bootp'
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `dhcp'
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `parse_allow_deny'
/usr/bin/ld: ../../common/.libs/libdhcp.so: undefined reference to `dhcp_set_control_state'

Need to add function definitions for these to the test code.