RFR: Fix unsupported configurations build after C2 changes

[Roman Kennke]

Am 25.06.2018 um 12:08 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/build/c2-sh/webrev.01/
> 
> Unsupported configurations do not build Shenandoah, and we need a few more conditionals in the new
> C2 code.
> 
> Testing: arm32, ppc64el, x86_64 build+tier1_gc_shenandoah
> 
> Thanks,
> -Aleksey
> 

Yes, thank you!

Roman