8134953: Make the GC ID available in a central place
Reviewed-by: pliden, jmasa

8087323: Unify and split the work gang classes
Reviewed-by: jmasa, sjohanss

8081682: AbstractWorkGang::_terminate is never used
Reviewed-by: kbarrett, pliden, brutisso

8079792: GC directory structure cleanup
Reviewed-by: brutisso, stefank, david