RFR [11], 2018-07-10, Bulk backports to sh/jdk11

[Aleksey Shipilev]

http://cr.openjdk.java.net/~shade/shenandoah/backports/jdk11-20180710/webrev.01/

This backports today's important fixes to sh/jdk11:

 [backport] Micro-optimize AArch64 assembly write-barriers
 [backport] Remove C2 write-barrier from .ad files
 [backport] Assembler write barriers should consistently check for forwarded objects
 [backport] Re-add Shenandoah TLAB allocation in aarch64 assembly
 [backport] Use correct 2-/3-op form of logical_and and put mask in register in C1 write-barrier
 [backport] Bind entry and jump to continuation in aarch64 write-barrier stub
 [backport] Fail when -XX:+UseShenandoahGC is used on unsupported platform
 [backport] Consolidate assembly write barriers

Testing: tier3_gc_shenandoah {fastdebug|release}, aarch64 hello world

(sh/jdk nightly is running with these patches, I'll push if that nightly is clean)

Thanks,
-Aleksey