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wget https://raw.githubusercontent.com/libbitcoin/libbitcoin/version3/install.sh
This one works flawlessly.
The README at https://github.com/libbitcoin/libbitcoin-node/tree/version3 does not have that wget fetch. It has links to the correct install.sh though,I just didn´t see it right away.
What I did then, I cloned the repo with the link on the github-page
git clone https://github.com/libbitcoin/libbitcoin-node.git
which gave me a version that doesn´t build. It´s working now.