Don't LDADD the xfr library for the resolver.
This was probably just a copy and paste mistake.
I brought this up on jabber a few days ago.
b10_resolver_LDADD += $(top_builddir)/src/lib/exceptions/libb10-exceptions.la
b10_resolver_LDADD += $(top_builddir)/src/lib/asiodns/libb10-asiodns.la
b10_resolver_LDADD += $(top_builddir)/src/lib/asiolink/libb10-asiolink.la
-b10_resolver_LDADD += $(top_builddir)/src/lib/xfr/libb10-xfr.la
b10_resolver_LDADD += $(top_builddir)/src/lib/log/libb10-log.la
b10_resolver_LDADD += $(top_builddir)/src/lib/server_common/libb10-server-common.la
b10_resolver_LDADD += $(top_builddir)/src/lib/cache/libb10-cache.la
run_unittests_LDADD += $(top_builddir)/src/lib/acl/libb10-dnsacl.la
run_unittests_LDADD += $(top_builddir)/src/lib/cc/libb10-cc.la
run_unittests_LDADD += $(top_builddir)/src/lib/exceptions/libb10-exceptions.la
-run_unittests_LDADD += $(top_builddir)/src/lib/xfr/libb10-xfr.la
run_unittests_LDADD += $(top_builddir)/src/lib/log/libb10-log.la
run_unittests_LDADD += $(top_builddir)/src/lib/server_common/libb10-server-common.la
run_unittests_LDADD += $(top_builddir)/src/lib/resolve/libb10-resolve.la