RFR: No variable-length arrays in standard C++

[Aleksey Shipilev]

Hi,

We use variable-length arrays in two places in GC code. This is not standard
C++, however. GCC has this extension and thus compiles fine, while MSVC fails. Fix:
  http://cr.openjdk.java.net/~shade/shenandoah/no-vla/webrev.01

Testing: hotspot_gc_shenandoah for 9 and 8u

Thanks,
-Aleksey