RFR: Fix Minimal VM build

[Roman Kennke]

Am 07.05.2018 um 13:46 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/minimal-vm/webrev.01/
> 
> This enables Shenandoah workspace to build cleanly with jvm-variant=minimal.
> 
> Testing: hotspot_gc_shenandoah {fastdebug|release} x86_64, {server,minimal} x86 build
> 
> Thanks,
> -Aleksey
> 

Ugh. All those #ifdefs ... but well ok, most of this stuff will
(hopefully) disappear again once we merge upstream c1 barrierset stuff.

Ok

Roman