Build generated sources before anything else
Build generated sources before anything else

Works for all, check, install targets but not for individual targets,
see ref: https://www.gnu.org/software/automake/manual/html_node/Built-Sources-Example.html

Fixes #2423

gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache