8215897: Build broken on zero after JDK-8211424

[Stefan Johansson]

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.

Thanks,
Stefan