We know that hwloc:external will be configured first (because of its
priority). Take advantage of that here in hwloc201 by having it
refuse to configure / politely fail if hwloc:external succeeded.
Also print out some additional lines in configure output indicating
what is going on (i.e., hwloc:external succeeded, so this component
will be skipped, or hwloc:external failed, so this component will be
used).
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
4e5f432786