build/gitlab-ci and build/travis-ci: add a 'make dist' step in autoconf_build()…
build/gitlab-ci and build/travis-ci: add a 'make dist' step in autoconf_build() target, to check we are release-ready
build/gitlab-ci and build/travis-ci: add a 'make dist' step in autoconf_build() target, to check we are release-ready