modules: Link to ivykis as well, if present.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
riemann: Move BUILT_SOURCES into the if branch

If we do not have the riemann-c-client available, don't try to build the
grammar, either, there's no point.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>