8215897: Build broken on zero after JDK-8211424

[Thomas Schatzl]

Hi,

On Sat, 2018-12-22 at 12:01 +0100, Stefan Johansson wrote:
> Hi,
> 
> Please review this fix for a build failure on Zero (or platforms 
> excluding G1 or Parallel).
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8215897
> Webrev: http://cr.openjdk.java.net/~sjohanss/8215897/00/
> 
> Summary
> The new whitebox methods for the AllocateOldGenAt feature was guarded
> by (G1 | Parallel), and this will not work if one of the GCs are not 
> present in the build.
> 
> Testing
> Built the previously failing platforms.

  looks good + trivial.

Thomas