8177963: Parallel GC fails fast when per-thread task log overflows
Summary: Instead of exiting the VM when per-thread task log overflows, print warnings once and ignore any further log addition attempt.
Reviewed-by: ysr, kbarrett, sangheki

8157240: GC task trace logging is incomprehensible
Reviewed-by: tschatzl, redestad

6858051: Create GC worker threads dynamically
Reviewed-by: tschatzl, drwhite

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