8033552: Fix missing missing volatile specifiers in CAS operations in GC code
Summary: Add missing volatile specifiers.
Reviewed-by: kbarrett, tschatzl

8151605: Change warning() to log_warning(gc) in the GC code
Reviewed-by: jwilhelm, jmasa

8148951: Remove unused method Generation::performs_in_place_marking()
Reviewed-by: david, jwilhelm

8145092: Use Unified Logging for the GC logging
Summary: JEP-271. VM changes contributed by brutisso, test changes contributed by david.
Reviewed-by: sjohanss, david, brutisso
Contributed-by: bengt.rutisson@oracle.com, david.lindholm@oralce.com

8139772: Cleanups in Generation related code
Reviewed-by: tbenson, mgerdin

8139434: Unify GenRemSet and CardTableRS
Reviewed-by: jwilhelm, mgerdin

8139506: Remove the WaterMark class
Reviewed-by: stefank, mgerdin

8134626: Misc cleanups after generation array removal
Reviewed-by: david, dholmes, tschatzl

8077842: Remove the level parameter passed around in GenCollectedHeap
Reviewed-by: kbarrett, mgerdin

8080112: Replace and remove the last usages of CollectedHeap::n_par_threads()
Reviewed-by: jmasa, kbarrett

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