RFR: [8] 2018-06-25: Bulk backports to sh/jdk8

[Roman Kennke]

Looks good too!
Roman

> http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk8u-20180625/webrev.01/
> 
> This backports recent performance and bugfixing work to sh/jdk8:
> 
>  [backport] Move (Java)Thread::_gc_state to lower offset to optimize barrier fast-path encoding
>  [backport] SH::make_(tlabs)_parsable() should work correctly with/without TLABs
>  [backport] Removed racy assertion
>  [backport] AlwaysPreTouch fails with non-default ConcGCThreads
>  [backport] Improve scheduling and interleaving of SATB processing in mark loop
>  [backport] Apply ShenandoahEvacOOMScope only for evac-taking paths in ShenandoahBarrierSet
>  [backport] Replace risky SBS::need_update_refs_barrier with straightforward check
>  [backport] Pre-filter oops before enqueing them in SBS slowpaths
>  [backport] SATB buffer filtering/compaction hides unmarked objects until final-mark
>  [backport] Process remaining SATB buffers in final mark/traverse loop instead of separate phase
>  [backport] Skip RESOLVE in SATBBufferClosure if no forwarded objects are in heap
>  [backport] VSC++ requires space(s) in between two string literals
>  [backport] Missing Shenandoah entry in GCNameHelper::to_string
> 
> Testing: hotspot_tier3_gc_shenandoah {fastdebug|release}
> 
> Thanks,
> -Aleksey
>