How to check for a specific language in gcc/tree.cc?

[Zopolis0]

8ff2a92a0450243e52d3299a13b30f208bafa7e0 has caused a severe regression
within GCJ, as it sets void_list_node in a different way to all of the
frontends.

Is there any way for me to check for Java in tree.cc and conditionally
set void_list_node based off of that?

As it stands, my best option is to revert 8ff2a92a entirely, which I would
prefer to avoid.