Merge

8210561: Command-line help wrong for javac --module Reviewed-by: darcy

8213299: runtime/appcds/jigsaw/classpathtests/EmptyClassInBootClassPath.java failed with java.lang.NoSuchMethodException Reviewed-by: dholmes

8215648: remove equals and hashCode implementations from j.l.i.VarHandle Reviewed-by: mchung

8216482: Shenandoah: typo in ShenandoahBarrierSetC2::clone_barrier_at_expansion() causes failed compilations Reviewed-by: thartmann, shade, rkennke

8215754: ZGC: nmethod is not unlinked from Method before rendezvous handshake Reviewed-by: pliden, neliasso

8216376: [PPC64] Possibly unreliable stack frame resizing in template interpreter Reviewed-by: goetz, gromero

8215244: jdk/jshell/ToolBasicTest.java testHistoryReference failed Summary: Mark history entries from previous sessions with timestamp that is definitelly in the past. Reviewed-by: rfield

8211841: [testbug] sun/nio/cs/OLD/TestIBMDB.java does not compile (aix) Reviewed-by: alanb, goetz

8215889: assert(!_unloading) failed: This oop is not available to unloading class loader data with ZGC Reviewed-by: coleenp, neliasso

8216401: Allow "file:" URLs in Class-Path of local JARs Reviewed-by: alanb, mchung

8215549: Shenandoah deduplication cleans up table/queue twice Reviewed-by: rkennke

8215482: check for cycles in type variables can provoke NPE Reviewed-by: mcimadamore

8216308: StackTraceElement::fill_in can use injected Class source-file Reviewed-by: coleenp, dholmes

8216265: [testbug] Introduce Platform.sharedLibraryPathVariableName() and adapt all tests. Summary: Also cleanup some switches over OSes and use File.pathSeparator. Reviewed-by: dholmes, mdoerr