Add :CHENEYGC feature to non-GENCGC targets.

Add :CHENEYGC feature to non-GENCGC targets.

  * When I wrote 14fd5afbac525e7a2e86903070afa0e94dfa14f7 I was
under the impression that there was a :CHENEYGC feature used on
plaforms that used the cheney collector.  This was logical, but
incorrect.

  * The two ways forward were to back out the use of :CHENEYGC
as a feature when checking compatibility or to move forward and
add :CHENEYGC and use it in preference to (NOT :GENCGC) where
appropriate, opening the door to a third GC option.

  * This is the minimal fix, adding :cheneygc to the non-gencgc
targets in make-config.sh.