Update libdns_la_LIBADD rather than libdns_la_LDFLAGS

the wrong macro was being update with MAXMINDDB_LIBS making
it difficult to adjust link order.
65 jobs for !6553 with 3445-update-libdns_la_libadd-instead-of-libdns_la_ldflags in 24 minutes and 16 seconds (queued for 13 minutes and 4 seconds)
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