Hugo Extended on CentOS 7

After first using the Hermit theme, I moved to the Hugo Coder theme to have a nicer front page and menu at the top. Unfortunately that needs Hugo in the “extended” version. The binary one can download on https://github.com/gohugoio/hugo/releases doesn’t run on CentOS 7, unlike the normal variant you get there (too new libstdc++ needed). One has to recompile it to get that working. To make it easier for others, to do so, just: