Make ART build/test configurations use the CC collector by default.

As the concurrent copying (CC) garbage collector is currently the
default GC in ART, set `ART_USE_READ_BARRIER` to `true` on most
build/test configurations, with the exception of configurations meant
to explicitly exercise a specific collector, GC configuration, heap
poisoning, or a build using Valgrind.

Test: Rely on ab/master-art-host builds.
Bug: 12687968
Change-Id: I6ef7d3ad668aa2d608f7e70794fb110aa65375ea