this is what i used to compile unbound for qnap (with libhiredis) for redis enabled cachedb backend

unbound-configure-for-qnap

## checkout unbound from:
## https://github.com/NLnetLabs/unbound

./configure \
--target=x86_64-pc-linux-gnu \
--host=x86_64-pc-linux-gnu \
--build=x86_64-pc-linux-gnu \
--program-prefix= \
--program-suffix= \
--prefix=/opt \
--bindir=/opt/bin \
--sbindir=/opt/sbin \
--libexecdir=/opt/lib \
--disable-flto \
--sysconfdir=/opt/etc \
--datadir=/opt/var/lib/unbound \
--localstatedir=/opt/var \
--with-chroot-dir \
--enable-allsymbols \
--enable-ipset \
--enable-ecdsa \
--enable-tfo-client \
--enable-tfo-server \
--with-libexpat=/opt \
--with-run-dir=/opt/var/lib/unbound \
--with-conf-file=/opt/etc/unbound/unbound.conf \
--with-pidfile=/opt/var/run/unbound.pid \
--enable-cachedb \
--with-ssl=/opt/local/openssl \
--with-libmnl=/opt \
--with-libhiredis=/opt/local \
--with-pthreads \
--enable-event-api \
--disable-gost \
--with-libevent

##
## prerequisite(s):
##   install: entware (+build packages)
##   install: redis-server
##   compile: openssl
##   compile: libevent
##

why would you disable flto or link time optimization? it would produce much slower binaries