RFR: [9] Bulk backports to sh/jdk9

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk9-20180514/webrev.01/

This backports recent work to sh/jdk9:

 [backport] Several small aarch64 fixes
 [backport] Critical native tests should only be ran on x86_64 platforms
 [backport] Fix Minimal VM build
 [backport] Fixing Windows and ARM32 build
 [backport] Fix ShFreeSet boundary case
 [backport] Cleanup: removed unused code
 [backport] Rename ShenandoahConcurrentThread to ShenandoahControlThread
 [backport] Break heuristics out from ShCollectorPolicy into their own source files

Testing: hotspot_gc_shenandoah {fastdebug|release}

Thanks,
-Aleksey